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 $169.76   7.553%   $182.582   $182.58   $182.60   $182.60  
  Purchase #2 $178.38   13.432%   $202.34   $202.34   $202.35   $202.30  
  Purchase #3 $68.42   9.748%   $75.0896   $75.09   $75.10   $75.10  
  Purchase #4 $82.56   7.361%   $88.6372   $88.64   $88.65   $88.60  
  Purchase #5 $82.75   4.693%   $86.6335   $86.63   $86.65   $86.60  
  Purchase #6 $180.67   10.166%   $199.0369   $199.04   $199.05   $199.00  
  Purchase #7 $22.30   9.326%   $24.3797   $24.38   $24.40   $24.40  
  7 purchase totals = $784.84       $858.6989   $858.70   $858.80   $858.60