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 $84.41   11.216%   $93.8774   $93.88   $93.90   $93.90  
  Purchase #2 $224.33   8.716%   $243.8826   $243.88   $243.90   $243.90  
  Purchase #3 $162.77   7.676%   $175.2642   $175.26   $175.25   $175.30  
  Purchase #4 $233.59   8.208%   $252.7631   $252.76   $252.75   $252.80  
  Purchase #5 $250.54   5.306%   $263.8337   $263.83   $263.85   $263.80  
  Purchase #6 $247.44   10.141%   $272.5329   $272.53   $272.55   $272.50  
  Purchase #7 $171.59   4.795%   $179.8177   $179.82   $179.80   $179.80  
  7 purchase totals = $1,374.67       $1,481.9716   $1,481.96   $1,482.00   $1,482.00