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 $11.92   13.684%   $13.5511   $13.55   $13.55   $13.60  
  Purchase #2 $226.95   12.624%   $255.6002   $255.60   $255.60   $255.60  
  Purchase #3 $235.97   3.511%   $244.2549   $244.25   $244.25   $244.30  
  Purchase #4 $99.54   5.393%   $104.9082   $104.91   $104.90   $104.90  
  Purchase #5 $136.54   4.210%   $142.2883   $142.29   $142.30   $142.30  
  Purchase #6 $184.77   12.190%   $207.2935   $207.29   $207.30   $207.30  
  Purchase #7 $72.50   5.675%   $76.6144   $76.61   $76.60   $76.60  
  7 purchase totals = $968.19       $1,044.5106   $1,044.50   $1,044.50   $1,044.60