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 $32.51   11.708%   $36.3163   $36.32   $36.30   $36.30  
  Purchase #2 $86.99   12.305%   $97.6941   $97.69   $97.70   $97.70  
  Purchase #3 $172.94   5.599%   $182.6229   $182.62   $182.60   $182.60  
  Purchase #4 $68.30   6.254%   $72.5715   $72.57   $72.55   $72.60  
  Purchase #5 $44.28   13.602%   $50.303   $50.30   $50.30   $50.30  
  Purchase #6 $106.99   13.104%   $121.01   $121.01   $121.00   $121.00  
  Purchase #7 $178.50   7.790%   $192.4052   $192.41   $192.40   $192.40  
  7 purchase totals = $690.51       $752.9230   $752.92   $752.85   $752.90