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 $60.74   10.319%   $67.0078   $67.01   $67.00   $67.00  
  Purchase #2 $34.96   7.387%   $37.5425   $37.54   $37.55   $37.50  
  Purchase #3 $73.66   7.733%   $79.3561   $79.36   $79.35   $79.40  
  Purchase #4 $66.79   8.836%   $72.6916   $72.69   $72.70   $72.70  
  Purchase #5 $202.78   13.286%   $229.7214   $229.72   $229.70   $229.70  
  Purchase #6 $108.89   8.525%   $118.1729   $118.17   $118.15   $118.20  
  Purchase #7 $248.40   5.384%   $261.7739   $261.77   $261.75   $261.80  
  7 purchase totals = $796.22       $866.2662   $866.26   $866.20   $866.30