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 $86.41   10.535%   $95.5133   $95.51   $95.50   $95.50  
  Purchase #2 $127.63   8.619%   $138.6304   $138.63   $138.65   $138.60  
  Purchase #3 $192.32   4.404%   $200.7898   $200.79   $200.80   $200.80  
  Purchase #4 $122.83   12.629%   $138.3422   $138.34   $138.35   $138.30  
  Purchase #5 $38.34   11.211%   $42.6383   $42.64   $42.65   $42.60  
  Purchase #6 $118.84   5.405%   $125.2633   $125.26   $125.25   $125.30  
  Purchase #7 $204.49   10.406%   $225.7692   $225.77   $225.75   $225.80  
  7 purchase totals = $890.86       $966.9465   $966.94   $966.95   $966.90