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 $95.38   5.227%   $100.3655   $100.37   $100.35   $100.40  
  Purchase #2 $82.81   4.743%   $86.7377   $86.74   $86.75   $86.70  
  Purchase #3 $205.25   9.352%   $224.445   $224.45   $224.45   $224.40  
  Purchase #4 $53.76   13.404%   $60.966   $60.97   $60.95   $61.00  
  Purchase #5 $192.28   5.824%   $203.4784   $203.48   $203.50   $203.50  
  Purchase #6 $146.54   6.844%   $156.5692   $156.57   $156.55   $156.60  
  Purchase #7 $72.57   8.344%   $78.6252   $78.63   $78.65   $78.60  
  7 purchase totals = $848.59       $911.1870   $911.21   $911.20   $911.20