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 $127.38   10.166%   $140.3295   $140.33   $140.35   $140.30  
  Purchase #2 $179.79   9.740%   $197.3015   $197.30   $197.30   $197.30  
  Purchase #3 $25.34   7.172%   $27.1574   $27.16   $27.15   $27.20  
  Purchase #4 $246.34   4.869%   $258.3343   $258.33   $258.35   $258.30  
  Purchase #5 $107.38   6.847%   $114.7323   $114.73   $114.75   $114.70  
  Purchase #6 $143.50   8.514%   $155.7176   $155.72   $155.70   $155.70  
  Purchase #7 $123.85   3.161%   $127.7649   $127.76   $127.75   $127.80  
  7 purchase totals = $953.58       $1,021.3375   $1,021.33   $1,021.35   $1,021.30