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 $32.77   7.275%   $35.154   $35.15   $35.15   $35.20  
  Purchase #2 $50.92   3.288%   $52.5942   $52.59   $52.60   $52.60  
  Purchase #3 $41.95   7.394%   $45.0518   $45.05   $45.05   $45.10  
  Purchase #4 $120.93   7.778%   $130.3359   $130.34   $130.35   $130.30  
  Purchase #5 $221.26   8.322%   $239.6733   $239.67   $239.65   $239.70  
  Purchase #6 $45.62   3.434%   $47.1866   $47.19   $47.20   $47.20  
  Purchase #7 $215.66   4.872%   $226.167   $226.17   $226.15   $226.20  
  7 purchase totals = $729.11       $776.1628   $776.16   $776.15   $776.30