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 $191.68   12.417%   $215.4809   $215.48   $215.50   $215.50  
  Purchase #2 $55.46   7.360%   $59.5419   $59.54   $59.55   $59.50  
  Purchase #3 $56.36   8.544%   $61.1754   $61.18   $61.20   $61.20  
  Purchase #4 $83.35   3.866%   $86.5723   $86.57   $86.55   $86.60  
  Purchase #5 $33.80   3.187%   $34.8772   $34.88   $34.90   $34.90  
  Purchase #6 $198.48   11.256%   $220.8209   $220.82   $220.80   $220.80  
  Purchase #7 $236.44   6.866%   $252.674   $252.67   $252.65   $252.70  
  7 purchase totals = $855.57       $931.1426   $931.14   $931.15   $931.20