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 $114.92   8.808%   $125.0422   $125.04   $125.05   $125.00  
  Purchase #2 $101.82   10.306%   $112.3136   $112.31   $112.30   $112.30  
  Purchase #3 $51.38   4.307%   $53.5929   $53.59   $53.60   $53.60  
  Purchase #4 $176.70   4.109%   $183.9606   $183.96   $183.95   $184.00  
  Purchase #5 $80.80   7.653%   $86.9836   $86.98   $87.00   $87.00  
  Purchase #6 $103.40   5.609%   $109.1997   $109.20   $109.20   $109.20  
  Purchase #7 $189.78   10.580%   $209.8587   $209.86   $209.85   $209.90  
  7 purchase totals = $818.80       $880.9513   $880.94   $880.95   $881.00