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 $211.52   10.546%   $233.8269   $233.83   $233.85   $233.80  
  Purchase #2 $236.84   12.546%   $266.5539   $266.55   $266.55   $266.60  
  Purchase #3 $126.53   12.726%   $142.6322   $142.63   $142.65   $142.60  
  Purchase #4 $241.90   11.716%   $270.241   $270.24   $270.25   $270.20  
  Purchase #5 $227.47   11.463%   $253.5449   $253.54   $253.55   $253.50  
  Purchase #6 $8.70   9.175%   $9.4982   $9.50   $9.50   $9.50  
  Purchase #7 $133.68   4.401%   $139.5633   $139.56   $139.55   $139.60  
  7 purchase totals = $1,186.64       $1,315.8604   $1,315.85   $1,315.90   $1,315.80