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 $57.53   6.117%   $61.0491   $61.05   $61.05   $61.00  
  Purchase #2 $241.73   9.110%   $263.7516   $263.75   $263.75   $263.80  
  Purchase #3 $100.77   4.634%   $105.4397   $105.44   $105.45   $105.40  
  Purchase #4 $78.48   9.147%   $85.6586   $85.66   $85.65   $85.70  
  Purchase #5 $53.98   9.190%   $58.9408   $58.94   $58.95   $58.90  
  Purchase #6 $104.90   3.745%   $108.8285   $108.83   $108.85   $108.80  
  Purchase #7 $141.51   11.431%   $157.686   $157.69   $157.70   $157.70  
  7 purchase totals = $778.90       $841.3543   $841.36   $841.40   $841.30