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 $217.41   3.202%   $224.3715   $224.37   $224.35   $224.40  
  Purchase #2 $211.98   13.845%   $241.3286   $241.33   $241.35   $241.30  
  Purchase #3 $182.86   12.364%   $205.4688   $205.47   $205.45   $205.50  
  Purchase #4 $193.71   5.649%   $204.6527   $204.65   $204.65   $204.70  
  Purchase #5 $118.42   8.286%   $128.2323   $128.23   $128.25   $128.20  
  Purchase #6 $168.95   11.811%   $188.9047   $188.90   $188.90   $188.90  
  Purchase #7 $31.97   9.560%   $35.0263   $35.03   $35.05   $35.00  
  7 purchase totals = $1,125.30       $1,227.9849   $1,227.98   $1,228.00   $1,228.00