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 $85.73   9.284%   $93.6892   $93.69   $93.70   $93.70  
  Purchase #2 $144.58   10.189%   $159.3113   $159.31   $159.30   $159.30  
  Purchase #3 $165.87   4.617%   $173.5282   $173.53   $173.55   $173.50  
  Purchase #4 $58.33   4.577%   $60.9998   $61.00   $61.00   $61.00  
  Purchase #5 $158.40   12.427%   $178.0844   $178.08   $178.10   $178.10  
  Purchase #6 $213.76   10.809%   $236.8653   $236.87   $236.85   $236.90  
  Purchase #7 $217.86   10.428%   $240.5784   $240.58   $240.60   $240.60  
  7 purchase totals = $1,044.53       $1,143.0566   $1,143.06   $1,143.10   $1,143.10