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 $145.60   13.784%   $165.6695   $165.67   $165.65   $165.70  
  Purchase #2 $245.55   8.857%   $267.2984   $267.30   $267.30   $267.30  
  Purchase #3 $230.43   13.382%   $261.2661   $261.27   $261.25   $261.30  
  Purchase #4 $104.90   6.472%   $111.6891   $111.69   $111.70   $111.70  
  Purchase #5 $119.93   12.834%   $135.3218   $135.32   $135.30   $135.30  
  Purchase #6 $35.67   10.441%   $39.3943   $39.39   $39.40   $39.40  
  Purchase #7 $250.82   4.146%   $261.219   $261.22   $261.20   $261.20  
  7 purchase totals = $1,132.90       $1,241.8582   $1,241.86   $1,241.80   $1,241.90