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 $61.33   6.627%   $65.3943   $65.39   $65.40   $65.40  
  Purchase #2 $185.49   5.627%   $195.9275   $195.93   $195.95   $195.90  
  Purchase #3 $228.49   9.413%   $249.9978   $250.00   $250.00   $250.00  
  Purchase #4 $204.96   13.432%   $232.4902   $232.49   $232.50   $232.50  
  Purchase #5 $110.40   7.841%   $119.0565   $119.06   $119.05   $119.10  
  Purchase #6 $87.47   8.538%   $94.9382   $94.94   $94.95   $94.90  
  Purchase #7 $117.75   6.610%   $125.5333   $125.53   $125.55   $125.50  
  7 purchase totals = $995.89       $1,083.3378   $1,083.34   $1,083.40   $1,083.30