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 $248.56   6.671%   $265.1414   $265.14   $265.15   $265.10  
  Purchase #2 $169.95   10.573%   $187.9188   $187.92   $187.90   $187.90  
  Purchase #3 $109.75   11.508%   $122.38   $122.38   $122.40   $122.40  
  Purchase #4 $59.95   6.414%   $63.7952   $63.80   $63.80   $63.80  
  Purchase #5 $167.59   4.125%   $174.5031   $174.50   $174.50   $174.50  
  Purchase #6 $216.76   10.430%   $239.3681   $239.37   $239.35   $239.40  
  Purchase #7 $29.52   9.176%   $32.2288   $32.23   $32.25   $32.20  
  7 purchase totals = $1,002.08       $1,085.3354   $1,085.34   $1,085.35   $1,085.30