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 $63.56   5.833%   $67.2675   $67.27   $67.25   $67.30  
  Purchase #2 $173.28   12.448%   $194.8499   $194.85   $194.85   $194.80  
  Purchase #3 $114.29   7.318%   $122.6537   $122.65   $122.65   $122.70  
  Purchase #4 $233.57   9.541%   $255.8549   $255.85   $255.85   $255.90  
  Purchase #5 $120.56   12.645%   $135.8048   $135.80   $135.80   $135.80  
  Purchase #6 $112.77   5.183%   $118.6149   $118.61   $118.60   $118.60  
  Purchase #7 $208.93   6.536%   $222.5857   $222.59   $222.60   $222.60  
  7 purchase totals = $1,026.96       $1,117.6314   $1,117.62   $1,117.60   $1,117.70