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 $43.66   8.850%   $47.5239   $47.52   $47.50   $47.50  
  Purchase #2 $168.60   8.386%   $182.7388   $182.74   $182.75   $182.70  
  Purchase #3 $129.53   8.848%   $140.9908   $140.99   $141.00   $141.00  
  Purchase #4 $222.37   11.130%   $247.1198   $247.12   $247.10   $247.10  
  Purchase #5 $87.25   12.212%   $97.905   $97.91   $97.90   $97.90  
  Purchase #6 $5.67   9.137%   $6.1881   $6.19   $6.20   $6.20  
  Purchase #7 $34.97   12.165%   $39.2241   $39.22   $39.20   $39.20  
  7 purchase totals = $692.05       $761.6905   $761.69   $761.65   $761.60