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 $56.83   10.286%   $62.6755   $62.68   $62.70   $62.70  
  Purchase #2 $250.68   8.146%   $271.1004   $271.10   $271.10   $271.10  
  Purchase #3 $102.27   9.721%   $112.2117   $112.21   $112.20   $112.20  
  Purchase #4 $28.93   5.310%   $30.4662   $30.47   $30.45   $30.50  
  Purchase #5 $58.82   4.330%   $61.3669   $61.37   $61.35   $61.40  
  Purchase #6 $11.42   5.274%   $12.0223   $12.02   $12.00   $12.00  
  Purchase #7 $154.74   4.852%   $162.248   $162.25   $162.25   $162.20  
  7 purchase totals = $663.69       $712.0910   $712.10   $712.05   $712.10