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 $124.46   12.803%   $140.3946   $140.39   $140.40   $140.40  
  Purchase #2 $67.35   12.494%   $75.7647   $75.76   $75.75   $75.80  
  Purchase #3 $157.42   7.807%   $169.7098   $169.71   $169.70   $169.70  
  Purchase #4 $24.46   6.717%   $26.103   $26.10   $26.10   $26.10  
  Purchase #5 $167.72   7.194%   $179.7858   $179.79   $179.80   $179.80  
  Purchase #6 $248.66   4.312%   $259.3822   $259.38   $259.40   $259.40  
  Purchase #7 $191.54   7.339%   $205.5971   $205.60   $205.60   $205.60  
  7 purchase totals = $981.61       $1,056.7372   $1,056.73   $1,056.75   $1,056.80