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 $180.61   13.210%   $204.4686   $204.47   $204.45   $204.50  
  Purchase #2 $106.62   11.592%   $118.9794   $118.98   $119.00   $119.00  
  Purchase #3 $221.30   3.804%   $229.7183   $229.72   $229.70   $229.70  
  Purchase #4 $94.69   13.775%   $107.7335   $107.73   $107.75   $107.70  
  Purchase #5 $216.40   6.802%   $231.1195   $231.12   $231.10   $231.10  
  Purchase #6 $242.87   3.347%   $250.9989   $251.00   $251.00   $251.00  
  Purchase #7 $62.36   11.432%   $69.489   $69.49   $69.50   $69.50  
  7 purchase totals = $1,124.85       $1,212.5072   $1,212.51   $1,212.50   $1,212.50