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 $105.99   8.264%   $114.749   $114.75   $114.75   $114.70  
  Purchase #2 $172.84   12.602%   $194.6213   $194.62   $194.60   $194.60  
  Purchase #3 $244.34   10.693%   $270.4673   $270.47   $270.45   $270.50  
  Purchase #4 $159.56   6.276%   $169.574   $169.57   $169.55   $169.60  
  Purchase #5 $60.45   12.211%   $67.8315   $67.83   $67.85   $67.80  
  Purchase #6 $221.67   12.380%   $249.1127   $249.11   $249.10   $249.10  
  Purchase #7 $60.48   3.529%   $62.6143   $62.61   $62.60   $62.60  
  7 purchase totals = $1,025.33       $1,128.9701   $1,128.96   $1,128.90   $1,128.90