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 $191.58   13.248%   $216.9605   $216.96   $216.95   $217.00  
  Purchase #2 $240.46   6.735%   $256.655   $256.66   $256.65   $256.70  
  Purchase #3 $58.50   4.287%   $61.0079   $61.01   $61.00   $61.00  
  Purchase #4 $32.52   10.869%   $36.0546   $36.05   $36.05   $36.10  
  Purchase #5 $188.34   7.644%   $202.7367   $202.74   $202.75   $202.70  
  Purchase #6 $226.48   12.592%   $254.9984   $255.00   $255.00   $255.00  
  Purchase #7 $208.75   5.354%   $219.9265   $219.93   $219.95   $219.90  
  7 purchase totals = $1,146.63       $1,248.3396   $1,248.35   $1,248.35   $1,248.40