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 $56.37   7.287%   $60.4777   $60.48   $60.50   $60.50  
  Purchase #2 $218.87   11.742%   $244.5697   $244.57   $244.55   $244.60  
  Purchase #3 $185.43   8.491%   $201.1749   $201.17   $201.15   $201.20  
  Purchase #4 $76.87   10.406%   $84.8691   $84.87   $84.85   $84.90  
  Purchase #5 $140.44   11.141%   $156.0864   $156.09   $156.10   $156.10  
  Purchase #6 $243.46   4.231%   $253.7608   $253.76   $253.75   $253.80  
  Purchase #7 $61.77   3.574%   $63.9777   $63.98   $64.00   $64.00  
  7 purchase totals = $983.21       $1,064.9163   $1,064.92   $1,064.90   $1,065.10