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 $65.51   13.676%   $74.4691   $74.47   $74.45   $74.50  
  Purchase #2 $154.71   3.771%   $160.5441   $160.54   $160.55   $160.50  
  Purchase #3 $244.32   13.673%   $277.7259   $277.73   $277.75   $277.70  
  Purchase #4 $20.25   8.615%   $21.9945   $21.99   $22.00   $22.00  
  Purchase #5 $209.85   10.205%   $231.2652   $231.27   $231.25   $231.30  
  Purchase #6 $217.45   8.761%   $236.5008   $236.50   $236.50   $236.50  
  Purchase #7 $136.73   9.706%   $150.001   $150.00   $150.00   $150.00  
  7 purchase totals = $1,048.82       $1,152.5006   $1,152.50   $1,152.50   $1,152.50