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 $126.99   4.422%   $132.6055   $132.61   $132.60   $132.60  
  Purchase #2 $228.62   11.386%   $254.6507   $254.65   $254.65   $254.70  
  Purchase #3 $159.31   6.384%   $169.4804   $169.48   $169.50   $169.50  
  Purchase #4 $225.94   5.747%   $238.9248   $238.92   $238.90   $238.90  
  Purchase #5 $35.28   3.251%   $36.427   $36.43   $36.45   $36.40  
  Purchase #6 $175.51   9.376%   $191.9658   $191.97   $191.95   $192.00  
  Purchase #7 $51.82   4.322%   $54.0597   $54.06   $54.05   $54.10  
  7 purchase totals = $1,003.47       $1,078.1139   $1,078.12   $1,078.10   $1,078.20