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 $238.92   8.541%   $259.3262   $259.33   $259.35   $259.30  
  Purchase #2 $123.85   8.653%   $134.5667   $134.57   $134.55   $134.60  
  Purchase #3 $93.84   3.735%   $97.3449   $97.34   $97.35   $97.30  
  Purchase #4 $100.46   4.181%   $104.6602   $104.66   $104.65   $104.70  
  Purchase #5 $112.45   9.583%   $123.2261   $123.23   $123.25   $123.20  
  Purchase #6 $88.51   7.221%   $94.9013   $94.90   $94.90   $94.90  
  Purchase #7 $238.51   3.439%   $246.7124   $246.71   $246.70   $246.70  
  7 purchase totals = $996.54       $1,060.7378   $1,060.74   $1,060.75   $1,060.70