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 $49.70   8.759%   $54.0532   $54.05   $54.05   $54.10  
  Purchase #2 $249.93   6.568%   $266.3454   $266.35   $266.35   $266.30  
  Purchase #3 $246.39   9.656%   $270.1814   $270.18   $270.20   $270.20  
  Purchase #4 $234.47   5.279%   $246.8477   $246.85   $246.85   $246.80  
  Purchase #5 $186.36   7.197%   $199.7723   $199.77   $199.75   $199.80  
  Purchase #6 $248.25   10.643%   $274.6712   $274.67   $274.65   $274.70  
  Purchase #7 $105.27   8.338%   $114.0474   $114.05   $114.05   $114.00  
  7 purchase totals = $1,320.37       $1,425.9186   $1,425.92   $1,425.90   $1,425.90