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 $87.98   9.113%   $95.9976   $96.00   $96.00   $96.00  
  Purchase #2 $58.49   7.266%   $62.7399   $62.74   $62.75   $62.70  
  Purchase #3 $139.29   6.626%   $148.5194   $148.52   $148.50   $148.50  
  Purchase #4 $173.79   4.673%   $181.9112   $181.91   $181.90   $181.90  
  Purchase #5 $189.35   11.174%   $210.508   $210.51   $210.50   $210.50  
  Purchase #6 $133.92   11.770%   $149.6824   $149.68   $149.70   $149.70  
  Purchase #7 $55.76   11.835%   $62.3592   $62.36   $62.35   $62.40  
  7 purchase totals = $838.58       $911.7177   $911.72   $911.70   $911.70