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 $54.61   13.462%   $61.9616   $61.96   $61.95   $62.00  
  Purchase #2 $16.97   7.772%   $18.2889   $18.29   $18.30   $18.30  
  Purchase #3 $9.37   4.436%   $9.7857   $9.79   $9.80   $9.80  
  Purchase #4 $194.34   6.498%   $206.9682   $206.97   $206.95   $207.00  
  Purchase #5 $161.98   7.421%   $174.0005   $174.00   $174.00   $174.00  
  Purchase #6 $64.57   3.794%   $67.0198   $67.02   $67.00   $67.00  
  Purchase #7 $149.26   11.673%   $166.6831   $166.68   $166.70   $166.70  
  7 purchase totals = $651.10       $704.7078   $704.71   $704.70   $704.80