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 $248.85   5.415%   $262.3252   $262.33   $262.35   $262.30  
  Purchase #2 $201.98   13.808%   $229.8694   $229.87   $229.85   $229.90  
  Purchase #3 $213.88   10.535%   $236.4123   $236.41   $236.40   $236.40  
  Purchase #4 $60.69   5.181%   $63.8343   $63.83   $63.85   $63.80  
  Purchase #5 $235.84   8.235%   $255.2614   $255.26   $255.25   $255.30  
  Purchase #6 $140.93   13.706%   $160.2459   $160.25   $160.25   $160.20  
  Purchase #7 $16.81   10.496%   $18.5744   $18.57   $18.55   $18.60  
  7 purchase totals = $1,118.98       $1,226.5229   $1,226.52   $1,226.50   $1,226.50