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 $211.87   10.583%   $234.2922   $234.29   $234.30   $234.30  
  Purchase #2 $247.59   11.117%   $275.1146   $275.11   $275.10   $275.10  
  Purchase #3 $57.52   3.365%   $59.4555   $59.46   $59.45   $59.50  
  Purchase #4 $235.92   12.398%   $265.1694   $265.17   $265.15   $265.20  
  Purchase #5 $102.50   3.793%   $106.3878   $106.39   $106.40   $106.40  
  Purchase #6 $187.54   8.388%   $203.2709   $203.27   $203.25   $203.30  
  Purchase #7 $69.29   7.796%   $74.6918   $74.69   $74.70   $74.70  
  7 purchase totals = $1,112.23       $1,218.3822   $1,218.38   $1,218.35   $1,218.50