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 $241.47   7.761%   $260.2105   $260.21   $260.20   $260.20  
  Purchase #2 $121.84   10.701%   $134.8781   $134.88   $134.90   $134.90  
  Purchase #3 $212.82   13.364%   $241.2613   $241.26   $241.25   $241.30  
  Purchase #4 $63.96   4.157%   $66.6188   $66.62   $66.60   $66.60  
  Purchase #5 $76.96   6.198%   $81.73   $81.73   $81.75   $81.70  
  Purchase #6 $197.44   8.643%   $214.5047   $214.50   $214.50   $214.50  
  Purchase #7 $41.95   7.774%   $45.2112   $45.21   $45.20   $45.20  
  7 purchase totals = $956.44       $1,044.4146   $1,044.41   $1,044.40   $1,044.40