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 $58.73   4.448%   $61.3423   $61.34   $61.35   $61.30  
  Purchase #2 $22.67   8.834%   $24.6727   $24.67   $24.65   $24.70  
  Purchase #3 $48.47   7.296%   $52.0064   $52.01   $52.00   $52.00  
  Purchase #4 $163.32   10.384%   $180.2791   $180.28   $180.30   $180.30  
  Purchase #5 $5.69   4.382%   $5.9393   $5.94   $5.95   $5.90  
  Purchase #6 $69.98   7.232%   $75.041   $75.04   $75.05   $75.00  
  Purchase #7 $245.71   5.485%   $259.1872   $259.19   $259.20   $259.20  
  7 purchase totals = $614.57       $658.4680   $658.47   $658.50   $658.40