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 $23.64   12.764%   $26.6574   $26.66   $26.65   $26.70  
  Purchase #2 $216.57   7.565%   $232.9535   $232.95   $232.95   $233.00  
  Purchase #3 $196.89   8.798%   $214.2124   $214.21   $214.20   $214.20  
  Purchase #4 $84.46   10.273%   $93.1366   $93.14   $93.15   $93.10  
  Purchase #5 $182.85   8.746%   $198.8421   $198.84   $198.85   $198.80  
  Purchase #6 $200.82   10.215%   $221.3338   $221.33   $221.35   $221.30  
  Purchase #7 $79.92   11.381%   $89.0157   $89.02   $89.00   $89.00  
  7 purchase totals = $985.15       $1,076.1515   $1,076.15   $1,076.15   $1,076.10