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 $183.63   11.255%   $204.2976   $204.30   $204.30   $204.30  
  Purchase #2 $141.46   8.721%   $153.7967   $153.80   $153.80   $153.80  
  Purchase #3 $223.37   13.519%   $253.5674   $253.57   $253.55   $253.60  
  Purchase #4 $159.62   10.231%   $175.9507   $175.95   $175.95   $176.00  
  Purchase #5 $175.57   8.296%   $190.1353   $190.14   $190.15   $190.10  
  Purchase #6 $240.77   6.368%   $256.1022   $256.10   $256.10   $256.10  
  Purchase #7 $55.26   10.460%   $61.0402   $61.04   $61.05   $61.00  
  7 purchase totals = $1,179.68       $1,294.8901   $1,294.90   $1,294.90   $1,294.90