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 $220.97   6.822%   $236.0446   $236.04   $236.05   $236.00  
  Purchase #2 $25.82   4.653%   $27.0214   $27.02   $27.00   $27.00  
  Purchase #3 $83.48   5.867%   $88.3778   $88.38   $88.40   $88.40  
  Purchase #4 $55.65   3.801%   $57.7653   $57.77   $57.75   $57.80  
  Purchase #5 $59.85   8.538%   $64.96   $64.96   $64.95   $65.00  
  Purchase #6 $15.69   3.609%   $16.2563   $16.26   $16.25   $16.30  
  Purchase #7 $238.74   12.449%   $268.4607   $268.46   $268.45   $268.50  
  7 purchase totals = $700.20       $758.8861   $758.89   $758.85   $759.00