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 $82.89   11.177%   $92.1546   $92.15   $92.15   $92.20  
  Purchase #2 $95.99   6.517%   $102.2457   $102.25   $102.25   $102.20  
  Purchase #3 $73.25   7.200%   $78.524   $78.52   $78.50   $78.50  
  Purchase #4 $62.52   9.181%   $68.26   $68.26   $68.25   $68.30  
  Purchase #5 $31.34   10.718%   $34.699   $34.70   $34.70   $34.70  
  Purchase #6 $248.26   9.543%   $271.9515   $271.95   $271.95   $272.00  
  Purchase #7 $214.65   6.781%   $229.2054   $229.21   $229.20   $229.20  
  7 purchase totals = $808.90       $877.0402   $877.04   $877.00   $877.10