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 $213.51   6.298%   $226.9569   $226.96   $226.95   $227.00  
  Purchase #2 $19.82   6.796%   $21.167   $21.17   $21.15   $21.20  
  Purchase #3 $125.89   3.300%   $130.0444   $130.04   $130.05   $130.00  
  Purchase #4 $18.25   11.596%   $20.3663   $20.37   $20.35   $20.40  
  Purchase #5 $240.44   5.188%   $252.914   $252.91   $252.90   $252.90  
  Purchase #6 $224.77   7.873%   $242.4661   $242.47   $242.45   $242.50  
  Purchase #7 $56.34   6.450%   $59.9739   $59.97   $59.95   $60.00  
  7 purchase totals = $899.02       $953.8886   $953.89   $953.80   $954.00