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 $58.93   12.738%   $66.4365   $66.44   $66.45   $66.40  
  Purchase #2 $123.55   4.692%   $129.347   $129.35   $129.35   $129.30  
  Purchase #3 $26.48   7.549%   $28.479   $28.48   $28.50   $28.50  
  Purchase #4 $49.60   13.598%   $56.3446   $56.34   $56.35   $56.30  
  Purchase #5 $167.33   11.149%   $185.9856   $185.99   $186.00   $186.00  
  Purchase #6 $41.48   8.184%   $44.8747   $44.87   $44.85   $44.90  
  Purchase #7 $77.52   5.843%   $82.0495   $82.05   $82.05   $82.00  
  7 purchase totals = $544.89       $593.5169   $593.52   $593.55   $593.40