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 $242.62   4.267%   $252.9726   $252.97   $252.95   $253.00  
  Purchase #2 $93.66   9.606%   $102.657   $102.66   $102.65   $102.70  
  Purchase #3 $103.41   6.838%   $110.4812   $110.48   $110.50   $110.50  
  Purchase #4 $200.65   13.375%   $227.4869   $227.49   $227.50   $227.50  
  Purchase #5 $239.52   8.706%   $260.3726   $260.37   $260.35   $260.40  
  Purchase #6 $61.59   8.624%   $66.9015   $66.90   $66.90   $66.90  
  Purchase #7 $78.43   5.774%   $82.9585   $82.96   $82.95   $83.00  
  7 purchase totals = $1,019.88       $1,103.8303   $1,103.83   $1,103.80   $1,104.00