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 $57.68   13.747%   $65.6093   $65.61   $65.60   $65.60  
  Purchase #2 $29.93   9.328%   $32.7219   $32.72   $32.70   $32.70  
  Purchase #3 $223.92   5.659%   $236.5916   $236.59   $236.60   $236.60  
  Purchase #4 $157.57   3.245%   $162.6831   $162.68   $162.70   $162.70  
  Purchase #5 $143.94   6.336%   $153.06   $153.06   $153.05   $153.10  
  Purchase #6 $52.30   8.341%   $56.6623   $56.66   $56.65   $56.70  
  Purchase #7 $171.35   4.429%   $178.9391   $178.94   $178.95   $178.90  
  7 purchase totals = $836.69       $886.2673   $886.26   $886.25   $886.30