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 $209.71   3.789%   $217.6559   $217.66   $217.65   $217.70  
  Purchase #2 $174.88   8.773%   $190.2222   $190.22   $190.20   $190.20  
  Purchase #3 $192.71   3.819%   $200.0696   $200.07   $200.05   $200.10  
  Purchase #4 $109.25   11.444%   $121.7526   $121.75   $121.75   $121.80  
  Purchase #5 $86.88   8.628%   $94.376   $94.38   $94.40   $94.40  
  Purchase #6 $108.34   13.131%   $122.5661   $122.57   $122.55   $122.60  
  Purchase #7 $247.67   12.451%   $278.5074   $278.51   $278.50   $278.50  
  7 purchase totals = $1,129.44       $1,225.1498   $1,225.16   $1,225.10   $1,225.30