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 $227.86   4.327%   $237.7195   $237.72   $237.70   $237.70  
  Purchase #2 $250.91   13.171%   $283.9574   $283.96   $283.95   $284.00  
  Purchase #3 $114.87   8.544%   $124.6845   $124.68   $124.70   $124.70  
  Purchase #4 $233.97   12.743%   $263.7848   $263.78   $263.80   $263.80  
  Purchase #5 $219.71   12.859%   $247.9625   $247.96   $247.95   $248.00  
  Purchase #6 $151.31   7.740%   $163.0214   $163.02   $163.00   $163.00  
  Purchase #7 $45.62   4.794%   $47.807   $47.81   $47.80   $47.80  
  7 purchase totals = $1,244.25       $1,368.9371   $1,368.93   $1,368.90   $1,369.00