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 $68.94   11.266%   $76.7068   $76.71   $76.70   $76.70  
  Purchase #2 $201.33   7.243%   $215.9123   $215.91   $215.90   $215.90  
  Purchase #3 $93.89   6.200%   $99.7112   $99.71   $99.70   $99.70  
  Purchase #4 $99.54   10.815%   $110.3053   $110.31   $110.30   $110.30  
  Purchase #5 $243.82   5.528%   $257.2984   $257.30   $257.30   $257.30  
  Purchase #6 $22.50   12.352%   $25.2792   $25.28   $25.30   $25.30  
  Purchase #7 $68.88   8.483%   $74.7231   $74.72   $74.70   $74.70  
  7 purchase totals = $798.90       $859.9363   $859.94   $859.90   $859.90