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 $67.53   10.673%   $74.7375   $74.74   $74.75   $74.70  
  Purchase #2 $177.64   4.486%   $185.6089   $185.61   $185.60   $185.60  
  Purchase #3 $194.41   4.629%   $203.4092   $203.41   $203.40   $203.40  
  Purchase #4 $239.94   10.747%   $265.7264   $265.73   $265.75   $265.70  
  Purchase #5 $227.78   8.529%   $247.2074   $247.21   $247.20   $247.20  
  Purchase #6 $201.91   6.462%   $214.9574   $214.96   $214.95   $215.00  
  Purchase #7 $91.63   9.427%   $100.268   $100.27   $100.25   $100.30  
  7 purchase totals = $1,200.84       $1,291.9148   $1,291.93   $1,291.90   $1,291.90