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 $64.74   11.680%   $72.3016   $72.30   $72.30   $72.30  
  Purchase #2 $217.69   8.472%   $236.1327   $236.13   $236.15   $236.10  
  Purchase #3 $130.79   7.183%   $140.1846   $140.18   $140.20   $140.20  
  Purchase #4 $228.41   4.811%   $239.3988   $239.40   $239.40   $239.40  
  Purchase #5 $119.96   13.174%   $135.7635   $135.76   $135.75   $135.80  
  Purchase #6 $192.36   3.562%   $199.2119   $199.21   $199.20   $199.20  
  Purchase #7 $23.57   12.572%   $26.5332   $26.53   $26.55   $26.50  
  7 purchase totals = $977.52       $1,049.5263   $1,049.51   $1,049.55   $1,049.50