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 $24.71   8.376%   $26.7797   $26.78   $26.80   $26.80  
  Purchase #2 $219.42   12.452%   $246.7422   $246.74   $246.75   $246.70  
  Purchase #3 $132.62   12.318%   $148.9561   $148.96   $148.95   $149.00  
  Purchase #4 $151.46   11.377%   $168.6916   $168.69   $168.70   $168.70  
  Purchase #5 $227.95   5.707%   $240.9591   $240.96   $240.95   $241.00  
  Purchase #6 $188.57   3.694%   $195.5358   $195.54   $195.55   $195.50  
  Purchase #7 $50.36   11.644%   $56.2239   $56.22   $56.20   $56.20  
  7 purchase totals = $995.09       $1,083.8884   $1,083.89   $1,083.90   $1,083.90