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 $215.77   8.459%   $234.022   $234.02   $234.00   $234.00  
  Purchase #2 $14.56   11.676%   $16.26   $16.26   $16.25   $16.30  
  Purchase #3 $211.61   10.818%   $234.502   $234.50   $234.50   $234.50  
  Purchase #4 $91.57   6.420%   $97.4488   $97.45   $97.45   $97.40  
  Purchase #5 $43.78   6.434%   $46.5968   $46.60   $46.60   $46.60  
  Purchase #6 $68.79   10.230%   $75.8272   $75.83   $75.85   $75.80  
  Purchase #7 $30.50   13.132%   $34.5053   $34.51   $34.50   $34.50  
  7 purchase totals = $676.58       $739.1621   $739.17   $739.15   $739.10