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 $211.66   13.669%   $240.5918   $240.59   $240.60   $240.60  
  Purchase #2 $56.56   9.544%   $61.9581   $61.96   $61.95   $62.00  
  Purchase #3 $233.78   8.575%   $253.8266   $253.83   $253.85   $253.80  
  Purchase #4 $114.76   5.238%   $120.7711   $120.77   $120.75   $120.80  
  Purchase #5 $22.47   4.141%   $23.4005   $23.40   $23.40   $23.40  
  Purchase #6 $223.57   8.170%   $241.8357   $241.84   $241.85   $241.80  
  Purchase #7 $230.98   12.276%   $259.3351   $259.34   $259.35   $259.30  
  7 purchase totals = $1,093.78       $1,201.7189   $1,201.73   $1,201.75   $1,201.70