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 $208.95   6.777%   $223.1105   $223.11   $223.10   $223.10  
  Purchase #2 $152.31   3.352%   $157.4154   $157.42   $157.40   $157.40  
  Purchase #3 $186.67   10.485%   $206.2423   $206.24   $206.25   $206.20  
  Purchase #4 $62.60   11.141%   $69.5743   $69.57   $69.55   $69.60  
  Purchase #5 $186.90   3.158%   $192.8023   $192.80   $192.80   $192.80  
  Purchase #6 $9.74   6.633%   $10.3861   $10.39   $10.40   $10.40  
  Purchase #7 $146.90   8.746%   $159.7479   $159.75   $159.75   $159.70  
  7 purchase totals = $954.07       $1,019.2788   $1,019.28   $1,019.25   $1,019.20