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 $241.82   9.427%   $264.6164   $264.62   $264.60   $264.60  
  Purchase #2 $150.52   4.488%   $157.2753   $157.28   $157.30   $157.30  
  Purchase #3 $14.32   7.445%   $15.3861   $15.39   $15.40   $15.40  
  Purchase #4 $129.92   4.652%   $135.9639   $135.96   $135.95   $136.00  
  Purchase #5 $190.86   12.193%   $214.1316   $214.13   $214.15   $214.10  
  Purchase #6 $113.89   12.560%   $128.1946   $128.19   $128.20   $128.20  
  Purchase #7 $36.36   8.807%   $39.5622   $39.56   $39.55   $39.60  
  7 purchase totals = $877.69       $955.1301   $955.13   $955.15   $955.20