Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.74   10.437%   $264.7617   $264.76   $264.75   $264.80  
  Purchase #2 $174.53   11.273%   $194.2048   $194.20   $194.20   $194.20  
  Purchase #3 $153.62   11.749%   $171.6688   $171.67   $171.65   $171.70  
  Purchase #4 $156.28   11.349%   $174.0162   $174.02   $174.00   $174.00  
  Purchase #5 $98.32   6.516%   $104.7265   $104.73   $104.75   $104.70  
  Purchase #6 $240.54   7.254%   $257.9888   $257.99   $258.00   $258.00  
  Purchase #7 $239.95   11.356%   $267.1987   $267.20   $267.20   $267.20  
  7 purchase totals = $1,302.98       $1,434.5655   $1,434.57   $1,434.55   $1,434.60