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 $158.60   8.238%   $171.6655   $171.67   $171.65   $171.70  
  Purchase #2 $242.71   10.483%   $268.1533   $268.15   $268.15   $268.20  
  Purchase #3 $63.34   8.753%   $68.8842   $68.88   $68.90   $68.90  
  Purchase #4 $202.97   5.671%   $214.4804   $214.48   $214.50   $214.50  
  Purchase #5 $14.27   6.282%   $15.1664   $15.17   $15.15   $15.20  
  Purchase #6 $244.44   4.836%   $256.2611   $256.26   $256.25   $256.30  
  Purchase #7 $22.93   7.376%   $24.6213   $24.62   $24.60   $24.60  
  7 purchase totals = $949.26       $1,019.2322   $1,019.23   $1,019.20   $1,019.40