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 $57.39   10.117%   $63.1961   $63.20   $63.20   $63.20  
  Purchase #2 $193.66   6.689%   $206.6139   $206.61   $206.60   $206.60  
  Purchase #3 $100.65   5.616%   $106.3025   $106.30   $106.30   $106.30  
  Purchase #4 $211.68   10.475%   $233.8535   $233.85   $233.85   $233.90  
  Purchase #5 $5.32   4.317%   $5.5497   $5.55   $5.55   $5.50  
  Purchase #6 $78.39   12.381%   $88.0955   $88.10   $88.10   $88.10  
  Purchase #7 $225.68   10.110%   $248.4962   $248.50   $248.50   $248.50  
  7 purchase totals = $872.77       $952.1074   $952.11   $952.10   $952.10