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 $186.83   10.813%   $207.0319   $207.03   $207.05   $207.00  
  Purchase #2 $200.48   7.243%   $215.0008   $215.00   $215.00   $215.00  
  Purchase #3 $100.61   13.854%   $114.5485   $114.55   $114.55   $114.50  
  Purchase #4 $33.29   6.793%   $35.5514   $35.55   $35.55   $35.60  
  Purchase #5 $148.93   12.617%   $167.7205   $167.72   $167.70   $167.70  
  Purchase #6 $194.30   3.207%   $200.5312   $200.53   $200.55   $200.50  
  Purchase #7 $178.92   13.372%   $202.8452   $202.85   $202.85   $202.80  
  7 purchase totals = $1,043.36       $1,143.2295   $1,143.23   $1,143.25   $1,143.10