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 $244.37   9.266%   $267.0133   $267.01   $267.00   $267.00  
  Purchase #2 $13.32   7.529%   $14.3229   $14.32   $14.30   $14.30  
  Purchase #3 $132.46   9.408%   $144.9218   $144.92   $144.90   $144.90  
  Purchase #4 $213.97   7.665%   $230.3708   $230.37   $230.35   $230.40  
  Purchase #5 $101.55   9.601%   $111.2998   $111.30   $111.30   $111.30  
  Purchase #6 $84.50   13.461%   $95.8745   $95.87   $95.85   $95.90  
  Purchase #7 $40.31   6.696%   $43.0092   $43.01   $43.00   $43.00  
  7 purchase totals = $830.48       $906.8123   $906.80   $906.70   $906.80