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 $18.85   7.149%   $20.1976   $20.20   $20.20   $20.20  
  Purchase #2 $160.41   8.545%   $174.117   $174.12   $174.10   $174.10  
  Purchase #3 $137.39   12.788%   $154.9594   $154.96   $154.95   $155.00  
  Purchase #4 $72.74   8.147%   $78.6661   $78.67   $78.65   $78.70  
  Purchase #5 $18.81   3.650%   $19.4966   $19.50   $19.50   $19.50  
  Purchase #6 $8.35   7.230%   $8.9537   $8.95   $8.95   $9.00  
  Purchase #7 $228.38   4.548%   $238.7667   $238.77   $238.75   $238.80  
  7 purchase totals = $644.93       $695.1571   $695.17   $695.10   $695.30