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 $234.48   9.405%   $256.5328   $256.53   $256.55   $256.50  
  Purchase #2 $131.95   13.336%   $149.5469   $149.55   $149.55   $149.50  
  Purchase #3 $157.57   9.452%   $172.4635   $172.46   $172.45   $172.50  
  Purchase #4 $126.96   5.650%   $134.1332   $134.13   $134.15   $134.10  
  Purchase #5 $142.87   13.106%   $161.5945   $161.59   $161.60   $161.60  
  Purchase #6 $236.57   8.494%   $256.6643   $256.66   $256.65   $256.70  
  Purchase #7 $217.78   7.179%   $233.4144   $233.41   $233.40   $233.40  
  7 purchase totals = $1,248.18       $1,364.3496   $1,364.33   $1,364.35   $1,364.30