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 $230.62   11.621%   $257.4204   $257.42   $257.40   $257.40  
  Purchase #2 $194.85   8.584%   $211.5759   $211.58   $211.60   $211.60  
  Purchase #3 $68.40   7.161%   $73.2981   $73.30   $73.30   $73.30  
  Purchase #4 $154.32   9.225%   $168.556   $168.56   $168.55   $168.60  
  Purchase #5 $125.32   5.220%   $131.8617   $131.86   $131.85   $131.90  
  Purchase #6 $148.91   11.440%   $165.9453   $165.95   $165.95   $165.90  
  Purchase #7 $140.97   9.636%   $154.5539   $154.55   $154.55   $154.60  
  7 purchase totals = $1,063.39       $1,163.2113   $1,163.22   $1,163.20   $1,163.30