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 $106.87   12.206%   $119.9146   $119.91   $119.90   $119.90  
  Purchase #2 $5.78   12.329%   $6.4926   $6.49   $6.50   $6.50  
  Purchase #3 $45.58   7.489%   $48.9935   $48.99   $49.00   $49.00  
  Purchase #4 $212.94   8.773%   $231.6212   $231.62   $231.60   $231.60  
  Purchase #5 $57.60   12.375%   $64.728   $64.73   $64.75   $64.70  
  Purchase #6 $91.40   10.487%   $100.9851   $100.99   $101.00   $101.00  
  Purchase #7 $177.54   5.223%   $186.8129   $186.81   $186.80   $186.80  
  7 purchase totals = $697.71       $759.5479   $759.54   $759.55   $759.50