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 $188.63   13.748%   $214.5629   $214.56   $214.55   $214.60  
  Purchase #2 $211.36   11.468%   $235.5988   $235.60   $235.60   $235.60  
  Purchase #3 $57.66   8.740%   $62.6995   $62.70   $62.70   $62.70  
  Purchase #4 $97.45   10.376%   $107.5614   $107.56   $107.55   $107.60  
  Purchase #5 $132.33   12.779%   $149.2405   $149.24   $149.25   $149.20  
  Purchase #6 $91.55   6.522%   $97.5209   $97.52   $97.50   $97.50  
  Purchase #7 $88.56   4.670%   $92.6958   $92.70   $92.70   $92.70  
  7 purchase totals = $867.54       $959.8798   $959.88   $959.85   $959.90