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 $87.60   6.328%   $93.1433   $93.14   $93.15   $93.10  
  Purchase #2 $185.27   12.828%   $209.0364   $209.04   $209.05   $209.00  
  Purchase #3 $95.55   12.477%   $107.4718   $107.47   $107.45   $107.50  
  Purchase #4 $53.34   13.459%   $60.519   $60.52   $60.50   $60.50  
  Purchase #5 $101.28   13.269%   $114.7188   $114.72   $114.70   $114.70  
  Purchase #6 $53.72   5.385%   $56.6128   $56.61   $56.60   $56.60  
  Purchase #7 $156.70   10.597%   $173.3055   $173.31   $173.30   $173.30  
  7 purchase totals = $733.46       $814.8076   $814.81   $814.75   $814.70