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 $232.31   5.320%   $244.6689   $244.67   $244.65   $244.70  
  Purchase #2 $99.72   13.479%   $113.1613   $113.16   $113.15   $113.20  
  Purchase #3 $39.67   12.659%   $44.6918   $44.69   $44.70   $44.70  
  Purchase #4 $174.57   10.782%   $193.3921   $193.39   $193.40   $193.40  
  Purchase #5 $34.65   5.103%   $36.4182   $36.42   $36.40   $36.40  
  Purchase #6 $78.90   9.722%   $86.5707   $86.57   $86.55   $86.60  
  Purchase #7 $69.70   4.278%   $72.6818   $72.68   $72.70   $72.70  
  7 purchase totals = $729.52       $791.5848   $791.58   $791.55   $791.70