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 $231.33   13.409%   $262.349   $262.35   $262.35   $262.30  
  Purchase #2 $125.96   3.480%   $130.3434   $130.34   $130.35   $130.30  
  Purchase #3 $56.28   7.626%   $60.5719   $60.57   $60.55   $60.60  
  Purchase #4 $236.89   5.689%   $250.3667   $250.37   $250.35   $250.40  
  Purchase #5 $71.73   6.291%   $76.2425   $76.24   $76.25   $76.20  
  Purchase #6 $145.43   3.335%   $150.2801   $150.28   $150.30   $150.30  
  Purchase #7 $110.34   4.360%   $115.1508   $115.15   $115.15   $115.20  
  7 purchase totals = $977.96       $1,045.3044   $1,045.30   $1,045.30   $1,045.30