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 $116.47   5.874%   $123.3114   $123.31   $123.30   $123.30  
  Purchase #2 $171.30   13.157%   $193.8379   $193.84   $193.85   $193.80  
  Purchase #3 $30.99   5.614%   $32.7298   $32.73   $32.75   $32.70  
  Purchase #4 $148.65   11.286%   $165.4266   $165.43   $165.45   $165.40  
  Purchase #5 $129.49   5.748%   $136.9331   $136.93   $136.95   $136.90  
  Purchase #6 $227.54   11.372%   $253.4158   $253.42   $253.40   $253.40  
  Purchase #7 $59.93   11.650%   $66.9118   $66.91   $66.90   $66.90  
  7 purchase totals = $884.37       $972.5664   $972.57   $972.60   $972.40