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 $216.42   11.702%   $241.7455   $241.75   $241.75   $241.70  
  Purchase #2 $181.75   3.655%   $188.393   $188.39   $188.40   $188.40  
  Purchase #3 $9.40   4.629%   $9.8351   $9.84   $9.85   $9.80  
  Purchase #4 $162.76   11.552%   $181.562   $181.56   $181.55   $181.60  
  Purchase #5 $64.70   13.373%   $73.3523   $73.35   $73.35   $73.40  
  Purchase #6 $159.45   4.128%   $166.0321   $166.03   $166.05   $166.00  
  Purchase #7 $94.88   7.186%   $101.6981   $101.70   $101.70   $101.70  
  7 purchase totals = $889.36       $962.6181   $962.62   $962.65   $962.60