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 $58.88   3.481%   $60.9296   $60.93   $60.95   $60.90  
  Purchase #2 $67.45   7.134%   $72.2619   $72.26   $72.25   $72.30  
  Purchase #3 $98.95   7.521%   $106.392   $106.39   $106.40   $106.40  
  Purchase #4 $24.77   12.110%   $27.7696   $27.77   $27.75   $27.80  
  Purchase #5 $173.87   5.465%   $183.372   $183.37   $183.35   $183.40  
  Purchase #6 $14.98   13.328%   $16.9765   $16.98   $17.00   $17.00  
  Purchase #7 $113.62   10.760%   $125.8455   $125.85   $125.85   $125.80  
  7 purchase totals = $552.52       $593.5471   $593.55   $593.55   $593.60