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 $113.68   9.523%   $124.5057   $124.51   $124.50   $124.50  
  Purchase #2 $90.95   12.546%   $102.3606   $102.36   $102.35   $102.40  
  Purchase #3 $125.82   8.791%   $136.8808   $136.88   $136.90   $136.90  
  Purchase #4 $26.57   3.673%   $27.5459   $27.55   $27.55   $27.50  
  Purchase #5 $241.93   4.239%   $252.1854   $252.19   $252.20   $252.20  
  Purchase #6 $96.25   4.355%   $100.4417   $100.44   $100.45   $100.40  
  Purchase #7 $26.59   6.516%   $28.3226   $28.32   $28.30   $28.30  
  7 purchase totals = $721.79       $772.2427   $772.25   $772.25   $772.20