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 $217.40   8.229%   $235.2898   $235.29   $235.30   $235.30  
  Purchase #2 $87.67   8.280%   $94.9291   $94.93   $94.95   $94.90  
  Purchase #3 $174.55   4.384%   $182.2023   $182.20   $182.20   $182.20  
  Purchase #4 $110.55   4.783%   $115.8376   $115.84   $115.85   $115.80  
  Purchase #5 $244.89   11.277%   $272.5062   $272.51   $272.50   $272.50  
  Purchase #6 $62.99   5.708%   $66.5855   $66.59   $66.60   $66.60  
  Purchase #7 $46.25   7.118%   $49.5421   $49.54   $49.55   $49.50  
  7 purchase totals = $944.30       $1,016.8926   $1,016.90   $1,016.95   $1,016.80