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 $213.66   11.784%   $238.8377   $238.84   $238.85   $238.80  
  Purchase #2 $184.54   10.274%   $203.4996   $203.50   $203.50   $203.50  
  Purchase #3 $184.72   11.186%   $205.3828   $205.38   $205.40   $205.40  
  Purchase #4 $8.88   6.740%   $9.4785   $9.48   $9.50   $9.50  
  Purchase #5 $223.68   5.701%   $236.432   $236.43   $236.45   $236.40  
  Purchase #6 $31.30   5.639%   $33.065   $33.07   $33.05   $33.10  
  Purchase #7 $104.73   7.574%   $112.6623   $112.66   $112.65   $112.70  
  7 purchase totals = $951.51       $1,039.3579   $1,039.36   $1,039.40   $1,039.40