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 $23.68   11.841%   $26.4839   $26.48   $26.50   $26.50  
  Purchase #2 $33.25   4.761%   $34.833   $34.83   $34.85   $34.80  
  Purchase #3 $237.73   6.463%   $253.0945   $253.09   $253.10   $253.10  
  Purchase #4 $201.74   6.723%   $215.303   $215.30   $215.30   $215.30  
  Purchase #5 $182.86   12.153%   $205.083   $205.08   $205.10   $205.10  
  Purchase #6 $241.29   5.619%   $254.8481   $254.85   $254.85   $254.80  
  Purchase #7 $155.69   11.778%   $174.0272   $174.03   $174.05   $174.00  
  7 purchase totals = $1,076.24       $1,163.6727   $1,163.66   $1,163.75   $1,163.60