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 $174.85   6.254%   $185.7851   $185.79   $185.80   $185.80  
  Purchase #2 $176.70   10.590%   $195.4125   $195.41   $195.40   $195.40  
  Purchase #3 $10.40   7.693%   $11.2001   $11.20   $11.20   $11.20  
  Purchase #4 $192.51   11.588%   $214.8181   $214.82   $214.80   $214.80  
  Purchase #5 $194.90   5.695%   $205.9996   $206.00   $206.00   $206.00  
  Purchase #6 $37.63   6.158%   $39.9473   $39.95   $39.95   $39.90  
  Purchase #7 $204.64   7.839%   $220.6817   $220.68   $220.70   $220.70  
  7 purchase totals = $991.63       $1,073.8444   $1,073.85   $1,073.85   $1,073.80