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 $136.33   11.615%   $152.1647   $152.16   $152.15   $152.20  
  Purchase #2 $193.71   9.276%   $211.6785   $211.68   $211.70   $211.70  
  Purchase #3 $151.92   10.329%   $167.6118   $167.61   $167.60   $167.60  
  Purchase #4 $68.72   9.541%   $75.2766   $75.28   $75.30   $75.30  
  Purchase #5 $81.58   8.720%   $88.6938   $88.69   $88.70   $88.70  
  Purchase #6 $158.49   12.831%   $178.8259   $178.83   $178.85   $178.80  
  Purchase #7 $65.45   7.651%   $70.4576   $70.46   $70.45   $70.50  
  7 purchase totals = $856.20       $944.7089   $944.71   $944.75   $944.80