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 $66.93   4.557%   $69.98   $69.98   $70.00   $70.00  
  Purchase #2 $195.35   9.133%   $213.1913   $213.19   $213.20   $213.20  
  Purchase #3 $108.96   11.482%   $121.4708   $121.47   $121.45   $121.50  
  Purchase #4 $142.92   13.170%   $161.7426   $161.74   $161.75   $161.70  
  Purchase #5 $16.36   9.730%   $17.9518   $17.95   $17.95   $18.00  
  Purchase #6 $79.55   6.186%   $84.471   $84.47   $84.45   $84.50  
  Purchase #7 $136.62   11.216%   $151.9433   $151.94   $151.95   $151.90  
  7 purchase totals = $746.69       $820.7508   $820.74   $820.75   $820.80