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 $67.81   8.122%   $73.3175   $73.32   $73.30   $73.30  
  Purchase #2 $152.86   5.167%   $160.7583   $160.76   $160.75   $160.80  
  Purchase #3 $21.73   9.641%   $23.825   $23.83   $23.85   $23.80  
  Purchase #4 $85.49   12.263%   $95.9736   $95.97   $95.95   $96.00  
  Purchase #5 $53.88   11.846%   $60.2626   $60.26   $60.25   $60.30  
  Purchase #6 $227.63   9.607%   $249.4984   $249.50   $249.50   $249.50  
  Purchase #7 $9.79   11.787%   $10.9439   $10.94   $10.95   $10.90  
  7 purchase totals = $619.19       $674.5793   $674.58   $674.55   $674.60