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 $212.80   11.871%   $238.0615   $238.06   $238.05   $238.10  
  Purchase #2 $206.55   11.298%   $229.886   $229.89   $229.90   $229.90  
  Purchase #3 $160.27   8.727%   $174.2568   $174.26   $174.25   $174.30  
  Purchase #4 $144.77   12.235%   $162.4826   $162.48   $162.50   $162.50  
  Purchase #5 $60.77   7.494%   $65.3241   $65.32   $65.30   $65.30  
  Purchase #6 $73.71   11.215%   $81.9766   $81.98   $82.00   $82.00  
  Purchase #7 $77.75   10.863%   $86.196   $86.20   $86.20   $86.20  
  7 purchase totals = $936.62       $1,038.1836   $1,038.19   $1,038.20   $1,038.30