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 $73.68   12.133%   $82.6196   $82.62   $82.60   $82.60  
  Purchase #2 $53.82   11.445%   $59.9797   $59.98   $60.00   $60.00  
  Purchase #3 $195.62   7.678%   $210.6397   $210.64   $210.65   $210.60  
  Purchase #4 $27.76   9.699%   $30.4524   $30.45   $30.45   $30.50  
  Purchase #5 $226.60   6.364%   $241.0208   $241.02   $241.00   $241.00  
  Purchase #6 $220.42   5.654%   $232.8825   $232.88   $232.90   $232.90  
  Purchase #7 $140.33   4.271%   $146.3235   $146.32   $146.30   $146.30  
  7 purchase totals = $938.23       $1,003.9182   $1,003.91   $1,003.90   $1,003.90