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 $73.70   9.368%   $80.6042   $80.60   $80.60   $80.60  
  Purchase #2 $39.45   6.632%   $42.0663   $42.07   $42.05   $42.10  
  Purchase #3 $189.70   9.838%   $208.3627   $208.36   $208.35   $208.40  
  Purchase #4 $75.97   9.659%   $83.3079   $83.31   $83.30   $83.30  
  Purchase #5 $237.60   13.503%   $269.6831   $269.68   $269.70   $269.70  
  Purchase #6 $100.68   3.463%   $104.1665   $104.17   $104.15   $104.20  
  Purchase #7 $45.86   8.499%   $49.7576   $49.76   $49.75   $49.80  
  7 purchase totals = $762.96       $837.9483   $837.95   $837.90   $838.10