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 $246.94   3.535%   $255.6693   $255.67   $255.65   $255.70  
  Purchase #2 $59.41   8.657%   $64.5531   $64.55   $64.55   $64.60  
  Purchase #3 $104.88   3.307%   $108.3484   $108.35   $108.35   $108.30  
  Purchase #4 $220.80   6.515%   $235.1851   $235.19   $235.20   $235.20  
  Purchase #5 $31.72   7.393%   $34.0651   $34.07   $34.05   $34.10  
  Purchase #6 $60.39   6.170%   $64.1161   $64.12   $64.10   $64.10  
  Purchase #7 $31.62   5.537%   $33.3708   $33.37   $33.35   $33.40  
  7 purchase totals = $755.76       $795.3079   $795.32   $795.25   $795.40