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 $115.44   9.147%   $125.9993   $126.00   $126.00   $126.00  
  Purchase #2 $192.87   3.626%   $199.8635   $199.86   $199.85   $199.90  
  Purchase #3 $81.75   11.579%   $91.2158   $91.22   $91.20   $91.20  
  Purchase #4 $41.32   4.119%   $43.022   $43.02   $43.00   $43.00  
  Purchase #5 $97.45   10.456%   $107.6394   $107.64   $107.65   $107.60  
  Purchase #6 $173.78   6.159%   $184.4831   $184.48   $184.50   $184.50  
  Purchase #7 $105.42   13.413%   $119.56   $119.56   $119.55   $119.60  
  7 purchase totals = $808.03       $871.7831   $871.78   $871.75   $871.80