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 $60.30   11.153%   $67.0253   $67.03   $67.05   $67.00  
  Purchase #2 $214.77   6.266%   $228.2275   $228.23   $228.25   $228.20  
  Purchase #3 $101.50   7.294%   $108.9034   $108.90   $108.90   $108.90  
  Purchase #4 $51.42   10.508%   $56.8232   $56.82   $56.80   $56.80  
  Purchase #5 $127.83   5.853%   $135.3119   $135.31   $135.30   $135.30  
  Purchase #6 $104.33   5.684%   $110.2601   $110.26   $110.25   $110.30  
  Purchase #7 $132.81   3.767%   $137.813   $137.81   $137.80   $137.80  
  7 purchase totals = $792.96       $844.3644   $844.36   $844.35   $844.30