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 $178.46   9.447%   $195.3191   $195.32   $195.30   $195.30  
  Purchase #2 $234.43   9.869%   $257.5659   $257.57   $257.55   $257.60  
  Purchase #3 $165.38   5.508%   $174.4891   $174.49   $174.50   $174.50  
  Purchase #4 $57.82   7.184%   $61.9738   $61.97   $61.95   $62.00  
  Purchase #5 $180.47   11.171%   $200.6303   $200.63   $200.65   $200.60  
  Purchase #6 $12.25   3.404%   $12.667   $12.67   $12.65   $12.70  
  Purchase #7 $197.37   10.385%   $217.8669   $217.87   $217.85   $217.90  
  7 purchase totals = $1,026.18       $1,120.5121   $1,120.52   $1,120.45   $1,120.60