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 $51.63   13.549%   $58.6253   $58.63   $58.65   $58.60  
  Purchase #2 $223.61   8.645%   $242.9411   $242.94   $242.95   $242.90  
  Purchase #3 $170.50   5.519%   $179.9099   $179.91   $179.90   $179.90  
  Purchase #4 $112.39   11.822%   $125.6767   $125.68   $125.70   $125.70  
  Purchase #5 $195.61   13.364%   $221.7513   $221.75   $221.75   $221.80  
  Purchase #6 $14.44   13.810%   $16.4342   $16.43   $16.45   $16.40  
  Purchase #7 $187.85   13.675%   $213.5385   $213.54   $213.55   $213.50  
  7 purchase totals = $956.03       $1,058.8770   $1,058.88   $1,058.95   $1,058.80