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 $236.92   12.508%   $266.554   $266.55   $266.55   $266.60  
  Purchase #2 $67.39   8.466%   $73.0952   $73.10   $73.10   $73.10  
  Purchase #3 $195.88   11.395%   $218.2005   $218.20   $218.20   $218.20  
  Purchase #4 $32.76   4.287%   $34.1644   $34.16   $34.15   $34.20  
  Purchase #5 $49.36   5.759%   $52.2026   $52.20   $52.20   $52.20  
  Purchase #6 $56.74   4.589%   $59.3438   $59.34   $59.35   $59.30  
  Purchase #7 $194.87   5.403%   $205.3988   $205.40   $205.40   $205.40  
  7 purchase totals = $833.92       $908.9593   $908.95   $908.95   $909.00