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 $171.66   13.371%   $194.6127   $194.61   $194.60   $194.60  
  Purchase #2 $22.97   3.227%   $23.7112   $23.71   $23.70   $23.70  
  Purchase #3 $183.72   5.425%   $193.6868   $193.69   $193.70   $193.70  
  Purchase #4 $109.58   9.784%   $120.3013   $120.30   $120.30   $120.30  
  Purchase #5 $143.37   11.561%   $159.945   $159.95   $159.95   $159.90  
  Purchase #6 $226.95   9.573%   $248.6759   $248.68   $248.70   $248.70  
  Purchase #7 $52.56   4.140%   $54.736   $54.74   $54.75   $54.70  
  7 purchase totals = $910.81       $995.6689   $995.68   $995.70   $995.60