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 $239.69   11.388%   $266.9859   $266.99   $267.00   $267.00  
  Purchase #2 $213.98   5.273%   $225.2632   $225.26   $225.25   $225.30  
  Purchase #3 $123.46   12.232%   $138.5616   $138.56   $138.55   $138.60  
  Purchase #4 $209.56   5.518%   $221.1235   $221.12   $221.10   $221.10  
  Purchase #5 $71.41   10.440%   $78.8652   $78.87   $78.85   $78.90  
  Purchase #6 $241.95   3.156%   $249.5859   $249.59   $249.60   $249.60  
  Purchase #7 $46.74   11.571%   $52.1483   $52.15   $52.15   $52.10  
  7 purchase totals = $1,146.79       $1,232.5336   $1,232.54   $1,232.50   $1,232.60