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 $208.44   8.747%   $226.6722   $226.67   $226.65   $226.70  
  Purchase #2 $178.73   10.563%   $197.6092   $197.61   $197.60   $197.60  
  Purchase #3 $92.84   4.855%   $97.3474   $97.35   $97.35   $97.30  
  Purchase #4 $31.47   8.486%   $34.1405   $34.14   $34.15   $34.10  
  Purchase #5 $173.92   7.162%   $186.3762   $186.38   $186.40   $186.40  
  Purchase #6 $141.56   5.440%   $149.2609   $149.26   $149.25   $149.30  
  Purchase #7 $36.89   11.546%   $41.1493   $41.15   $41.15   $41.10  
  7 purchase totals = $863.85       $932.5557   $932.56   $932.55   $932.50