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 $181.98   12.833%   $205.3335   $205.33   $205.35   $205.30  
  Purchase #2 $161.46   9.430%   $176.6857   $176.69   $176.70   $176.70  
  Purchase #3 $240.53   5.520%   $253.8073   $253.81   $253.80   $253.80  
  Purchase #4 $168.93   6.524%   $179.951   $179.95   $179.95   $180.00  
  Purchase #5 $156.90   3.187%   $161.9004   $161.90   $161.90   $161.90  
  Purchase #6 $158.50   8.455%   $171.9012   $171.90   $171.90   $171.90  
  Purchase #7 $164.76   12.288%   $185.0057   $185.01   $185.00   $185.00  
  7 purchase totals = $1,233.06       $1,334.5848   $1,334.59   $1,334.60   $1,334.60