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 $86.74   10.285%   $95.6612   $95.66   $95.65   $95.70  
  Purchase #2 $204.33   12.738%   $230.3576   $230.36   $230.35   $230.40  
  Purchase #3 $226.49   10.479%   $250.2239   $250.22   $250.20   $250.20  
  Purchase #4 $41.64   10.209%   $45.891   $45.89   $45.90   $45.90  
  Purchase #5 $60.36   4.468%   $63.0569   $63.06   $63.05   $63.10  
  Purchase #6 $117.53   11.610%   $131.1752   $131.18   $131.20   $131.20  
  Purchase #7 $154.75   12.609%   $174.2624   $174.26   $174.25   $174.30  
  7 purchase totals = $891.84       $990.6282   $990.63   $990.60   $990.80