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 $52.29   8.515%   $56.7425   $56.74   $56.75   $56.70  
  Purchase #2 $61.37   4.323%   $64.023   $64.02   $64.00   $64.00  
  Purchase #3 $109.93   10.385%   $121.3462   $121.35   $121.35   $121.30  
  Purchase #4 $199.25   3.358%   $205.9408   $205.94   $205.95   $205.90  
  Purchase #5 $17.49   10.589%   $19.342   $19.34   $19.35   $19.30  
  Purchase #6 $233.48   8.797%   $254.0192   $254.02   $254.00   $254.00  
  Purchase #7 $11.90   11.761%   $13.2996   $13.30   $13.30   $13.30  
  7 purchase totals = $685.71       $734.7133   $734.71   $734.70   $734.50