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 $195.27   9.766%   $214.3401   $214.34   $214.35   $214.30  
  Purchase #2 $158.42   5.262%   $166.7561   $166.76   $166.75   $166.80  
  Purchase #3 $63.71   3.745%   $66.0959   $66.10   $66.10   $66.10  
  Purchase #4 $79.27   3.677%   $82.1848   $82.18   $82.20   $82.20  
  Purchase #5 $231.63   5.459%   $244.2747   $244.27   $244.25   $244.30  
  Purchase #6 $79.98   4.610%   $83.6671   $83.67   $83.65   $83.70  
  Purchase #7 $158.51   13.415%   $179.7741   $179.77   $179.75   $179.80  
  7 purchase totals = $966.79       $1,037.0928   $1,037.09   $1,037.05   $1,037.20