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 $236.65   13.447%   $268.4723   $268.47   $268.45   $268.50  
  Purchase #2 $95.79   10.237%   $105.596   $105.60   $105.60   $105.60  
  Purchase #3 $124.97   13.335%   $141.6347   $141.63   $141.65   $141.60  
  Purchase #4 $234.85   4.482%   $245.376   $245.38   $245.40   $245.40  
  Purchase #5 $169.60   6.448%   $180.5358   $180.54   $180.55   $180.50  
  Purchase #6 $108.93   11.193%   $121.1225   $121.12   $121.10   $121.10  
  Purchase #7 $130.37   9.564%   $142.8386   $142.84   $142.85   $142.80  
  7 purchase totals = $1,101.16       $1,205.5759   $1,205.58   $1,205.60   $1,205.50