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 $236.42   11.221%   $262.9487   $262.95   $262.95   $262.90  
  Purchase #2 $212.43   9.599%   $232.8212   $232.82   $232.80   $232.80  
  Purchase #3 $175.53   6.725%   $187.3344   $187.33   $187.35   $187.30  
  Purchase #4 $227.76   7.619%   $245.113   $245.11   $245.10   $245.10  
  Purchase #5 $45.60   6.146%   $48.4026   $48.40   $48.40   $48.40  
  Purchase #6 $187.26   9.736%   $205.4916   $205.49   $205.50   $205.50  
  Purchase #7 $166.56   13.234%   $188.6026   $188.60   $188.60   $188.60  
  7 purchase totals = $1,251.56       $1,370.7141   $1,370.70   $1,370.70   $1,370.60