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 $224.52   10.754%   $248.6649   $248.66   $248.65   $248.70  
  Purchase #2 $226.96   8.405%   $246.036   $246.04   $246.05   $246.00  
  Purchase #3 $143.45   7.680%   $154.467   $154.47   $154.45   $154.50  
  Purchase #4 $207.64   7.423%   $223.0531   $223.05   $223.05   $223.10  
  Purchase #5 $151.86   11.451%   $169.2495   $169.25   $169.25   $169.20  
  Purchase #6 $247.80   12.647%   $279.1393   $279.14   $279.15   $279.10  
  Purchase #7 $57.28   10.343%   $63.2045   $63.20   $63.20   $63.20  
  7 purchase totals = $1,259.51       $1,383.8143   $1,383.81   $1,383.80   $1,383.80