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 $193.63   10.104%   $213.1944   $213.19   $213.20   $213.20  
  Purchase #2 $81.40   4.679%   $85.2087   $85.21   $85.20   $85.20  
  Purchase #3 $109.38   9.222%   $119.467   $119.47   $119.45   $119.50  
  Purchase #4 $145.88   5.119%   $153.3476   $153.35   $153.35   $153.30  
  Purchase #5 $181.89   3.456%   $188.1761   $188.18   $188.20   $188.20  
  Purchase #6 $144.44   13.255%   $163.5855   $163.59   $163.60   $163.60  
  Purchase #7 $39.64   9.773%   $43.514   $43.51   $43.50   $43.50  
  7 purchase totals = $896.26       $966.4933   $966.50   $966.50   $966.50