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 $224.49   7.521%   $241.3739   $241.37   $241.35   $241.40  
  Purchase #2 $163.42   12.652%   $184.0959   $184.10   $184.10   $184.10  
  Purchase #3 $116.32   8.596%   $126.3189   $126.32   $126.30   $126.30  
  Purchase #4 $186.29   7.159%   $199.6265   $199.63   $199.65   $199.60  
  Purchase #5 $9.41   3.197%   $9.7108   $9.71   $9.70   $9.70  
  Purchase #6 $53.33   6.683%   $56.894   $56.89   $56.90   $56.90  
  Purchase #7 $113.30   9.780%   $124.3807   $124.38   $124.40   $124.40  
  7 purchase totals = $866.56       $942.4007   $942.40   $942.40   $942.40