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 $56.92   10.116%   $62.678   $62.68   $62.70   $62.70  
  Purchase #2 $66.72   4.809%   $69.9286   $69.93   $69.95   $69.90  
  Purchase #3 $190.99   9.427%   $208.9946   $208.99   $209.00   $209.00  
  Purchase #4 $209.88   7.728%   $226.0995   $226.10   $226.10   $226.10  
  Purchase #5 $50.42   4.709%   $52.7943   $52.79   $52.80   $52.80  
  Purchase #6 $144.70   11.544%   $161.4042   $161.40   $161.40   $161.40  
  Purchase #7 $58.79   5.452%   $61.9952   $62.00   $62.00   $62.00  
  7 purchase totals = $778.42       $843.8944   $843.89   $843.95   $843.90