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 $111.36   13.120%   $125.9704   $125.97   $125.95   $126.00  
  Purchase #2 $41.77   12.135%   $46.8388   $46.84   $46.85   $46.80  
  Purchase #3 $30.92   12.354%   $34.7399   $34.74   $34.75   $34.70  
  Purchase #4 $106.37   11.166%   $118.2473   $118.25   $118.25   $118.20  
  Purchase #5 $42.26   11.319%   $47.0434   $47.04   $47.05   $47.00  
  Purchase #6 $177.50   5.683%   $187.5873   $187.59   $187.60   $187.60  
  Purchase #7 $157.52   8.197%   $170.4319   $170.43   $170.45   $170.40  
  7 purchase totals = $667.70       $730.8590   $730.86   $730.90   $730.70