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 $51.41   13.307%   $58.2511   $58.25   $58.25   $58.30  
  Purchase #2 $163.36   6.455%   $173.9049   $173.90   $173.90   $173.90  
  Purchase #3 $200.89   5.470%   $211.8787   $211.88   $211.90   $211.90  
  Purchase #4 $156.27   3.661%   $161.991   $161.99   $162.00   $162.00  
  Purchase #5 $94.79   11.830%   $106.0037   $106.00   $106.00   $106.00  
  Purchase #6 $8.94   5.577%   $9.4386   $9.44   $9.45   $9.40  
  Purchase #7 $74.46   3.434%   $77.017   $77.02   $77.00   $77.00  
  7 purchase totals = $750.12       $798.4850   $798.48   $798.50   $798.50