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 $9.32   9.201%   $10.1775   $10.18   $10.20   $10.20  
  Purchase #2 $132.39   9.201%   $144.5712   $144.57   $144.55   $144.60  
  Purchase #3 $171.58   8.418%   $186.0236   $186.02   $186.00   $186.00  
  Purchase #4 $166.26   9.233%   $181.6108   $181.61   $181.60   $181.60  
  Purchase #5 $102.40   5.330%   $107.8579   $107.86   $107.85   $107.90  
  Purchase #6 $161.73   9.287%   $176.7499   $176.75   $176.75   $176.70  
  Purchase #7 $19.85   7.646%   $21.3677   $21.37   $21.35   $21.40  
  7 purchase totals = $763.53       $828.3586   $828.36   $828.30   $828.40