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 $228.46   8.646%   $248.2127   $248.21   $248.20   $248.20  
  Purchase #2 $184.25   8.312%   $199.5649   $199.56   $199.55   $199.60  
  Purchase #3 $148.81   12.461%   $167.3532   $167.35   $167.35   $167.40  
  Purchase #4 $33.52   12.166%   $37.598   $37.60   $37.60   $37.60  
  Purchase #5 $214.52   13.226%   $242.8924   $242.89   $242.90   $242.90  
  Purchase #6 $170.60   12.509%   $191.9404   $191.94   $191.95   $191.90  
  Purchase #7 $247.93   11.337%   $276.0378   $276.04   $276.05   $276.00  
  7 purchase totals = $1,228.09       $1,363.5994   $1,363.59   $1,363.60   $1,363.60