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 $139.70   7.587%   $150.299   $150.30   $150.30   $150.30  
  Purchase #2 $187.89   11.765%   $209.9953   $210.00   $210.00   $210.00  
  Purchase #3 $35.84   3.161%   $36.9729   $36.97   $36.95   $37.00  
  Purchase #4 $104.45   9.861%   $114.7498   $114.75   $114.75   $114.70  
  Purchase #5 $222.65   8.312%   $241.1567   $241.16   $241.15   $241.20  
  Purchase #6 $10.73   11.303%   $11.9428   $11.94   $11.95   $11.90  
  Purchase #7 $236.36   4.223%   $246.3415   $246.34   $246.35   $246.30  
  7 purchase totals = $937.62       $1,011.4580   $1,011.46   $1,011.45   $1,011.40