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 $204.56   13.513%   $232.2022   $232.20   $232.20   $232.20  
  Purchase #2 $167.57   13.506%   $190.202   $190.20   $190.20   $190.20  
  Purchase #3 $81.76   11.246%   $90.9547   $90.95   $90.95   $91.00  
  Purchase #4 $105.40   10.322%   $116.2794   $116.28   $116.30   $116.30  
  Purchase #5 $200.62   6.476%   $213.6122   $213.61   $213.60   $213.60  
  Purchase #6 $38.96   11.114%   $43.29   $43.29   $43.30   $43.30  
  Purchase #7 $140.62   4.385%   $146.7862   $146.79   $146.80   $146.80  
  7 purchase totals = $939.49       $1,033.3267   $1,033.32   $1,033.35   $1,033.40