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 $204.35   3.253%   $210.9975   $211.00   $211.00   $211.00  
  Purchase #2 $93.70   8.123%   $101.3113   $101.31   $101.30   $101.30  
  Purchase #3 $157.51   12.283%   $176.857   $176.86   $176.85   $176.90  
  Purchase #4 $96.44   12.165%   $108.1719   $108.17   $108.15   $108.20  
  Purchase #5 $144.80   10.265%   $159.6637   $159.66   $159.65   $159.70  
  Purchase #6 $105.38   7.391%   $113.1686   $113.17   $113.15   $113.20  
  Purchase #7 $34.87   4.471%   $36.429   $36.43   $36.45   $36.40  
  7 purchase totals = $837.05       $906.5990   $906.60   $906.55   $906.70