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 $97.72   8.514%   $106.0399   $106.04   $106.05   $106.00  
  Purchase #2 $176.97   13.547%   $200.9441   $200.94   $200.95   $200.90  
  Purchase #3 $33.63   3.702%   $34.875   $34.88   $34.90   $34.90  
  Purchase #4 $174.80   10.377%   $192.939   $192.94   $192.95   $192.90  
  Purchase #5 $158.47   10.685%   $175.4025   $175.40   $175.40   $175.40  
  Purchase #6 $60.67   6.110%   $64.3769   $64.38   $64.40   $64.40  
  Purchase #7 $203.55   6.701%   $217.1899   $217.19   $217.20   $217.20  
  7 purchase totals = $905.81       $991.7673   $991.77   $991.85   $991.70