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 $55.47   5.154%   $58.3289   $58.33   $58.35   $58.30  
  Purchase #2 $170.89   3.769%   $177.3308   $177.33   $177.35   $177.30  
  Purchase #3 $186.94   4.785%   $195.8851   $195.89   $195.90   $195.90  
  Purchase #4 $199.45   12.866%   $225.1112   $225.11   $225.10   $225.10  
  Purchase #5 $201.86   6.195%   $214.3652   $214.37   $214.35   $214.40  
  Purchase #6 $155.55   4.759%   $162.9526   $162.95   $162.95   $163.00  
  Purchase #7 $215.45   11.153%   $239.4791   $239.48   $239.50   $239.50  
  7 purchase totals = $1,185.61       $1,273.4529   $1,273.46   $1,273.50   $1,273.50