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 $58.45   11.752%   $65.319   $65.32   $65.30   $65.30  
  Purchase #2 $170.44   6.562%   $181.6243   $181.62   $181.60   $181.60  
  Purchase #3 $62.36   3.323%   $64.4322   $64.43   $64.45   $64.40  
  Purchase #4 $13.57   11.603%   $15.1445   $15.14   $15.15   $15.10  
  Purchase #5 $96.39   6.480%   $102.6361   $102.64   $102.65   $102.60  
  Purchase #6 $224.74   4.763%   $235.4444   $235.44   $235.45   $235.40  
  Purchase #7 $159.42   6.210%   $169.32   $169.32   $169.30   $169.30  
  7 purchase totals = $785.37       $833.9205   $833.91   $833.90   $833.70