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 $46.93   11.205%   $52.1885   $52.19   $52.20   $52.20  
  Purchase #2 $98.88   5.772%   $104.5874   $104.59   $104.60   $104.60  
  Purchase #3 $63.70   11.693%   $71.1484   $71.15   $71.15   $71.10  
  Purchase #4 $144.85   5.717%   $153.1311   $153.13   $153.15   $153.10  
  Purchase #5 $241.62   9.832%   $265.3761   $265.38   $265.40   $265.40  
  Purchase #6 $9.52   6.260%   $10.116   $10.12   $10.10   $10.10  
  Purchase #7 $176.73   9.300%   $193.1659   $193.17   $193.15   $193.20  
  7 purchase totals = $782.23       $849.7134   $849.73   $849.75   $849.70