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 $84.30   9.759%   $92.5268   $92.53   $92.55   $92.50  
  Purchase #2 $230.28   8.516%   $249.8906   $249.89   $249.90   $249.90  
  Purchase #3 $201.92   7.103%   $216.2624   $216.26   $216.25   $216.30  
  Purchase #4 $162.81   8.488%   $176.6293   $176.63   $176.65   $176.60  
  Purchase #5 $154.54   9.732%   $169.5798   $169.58   $169.60   $169.60  
  Purchase #6 $74.94   7.186%   $80.3252   $80.33   $80.35   $80.30  
  Purchase #7 $172.65   5.449%   $182.0577   $182.06   $182.05   $182.10  
  7 purchase totals = $1,081.44       $1,167.2718   $1,167.28   $1,167.35   $1,167.30