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 $157.73   3.141%   $162.6843   $162.68   $162.70   $162.70  
  Purchase #2 $53.43   3.678%   $55.3952   $55.40   $55.40   $55.40  
  Purchase #3 $32.39   3.282%   $33.453   $33.45   $33.45   $33.50  
  Purchase #4 $88.84   3.179%   $91.6642   $91.66   $91.65   $91.70  
  Purchase #5 $67.74   6.694%   $72.2745   $72.27   $72.25   $72.30  
  Purchase #6 $181.58   11.173%   $201.8679   $201.87   $201.85   $201.90  
  Purchase #7 $233.96   3.494%   $242.1346   $242.13   $242.15   $242.10  
  7 purchase totals = $815.67       $859.4737   $859.46   $859.45   $859.60