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 $173.90   10.500%   $192.1595   $192.16   $192.15   $192.20  
  Purchase #2 $243.96   8.353%   $264.338   $264.34   $264.35   $264.30  
  Purchase #3 $174.73   6.352%   $185.8288   $185.83   $185.85   $185.80  
  Purchase #4 $199.62   10.336%   $220.2527   $220.25   $220.25   $220.30  
  Purchase #5 $15.72   9.307%   $17.1831   $17.18   $17.20   $17.20  
  Purchase #6 $193.42   7.772%   $208.4526   $208.45   $208.45   $208.50  
  Purchase #7 $108.57   13.689%   $123.4321   $123.43   $123.45   $123.40  
  7 purchase totals = $1,109.92       $1,211.6468   $1,211.64   $1,211.70   $1,211.70