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 $155.79   7.535%   $167.5288   $167.53   $167.55   $167.50  
  Purchase #2 $186.97   11.252%   $208.0079   $208.01   $208.00   $208.00  
  Purchase #3 $164.56   13.860%   $187.368   $187.37   $187.35   $187.40  
  Purchase #4 $246.40   7.431%   $264.71   $264.71   $264.70   $264.70  
  Purchase #5 $6.29   9.711%   $6.9008   $6.90   $6.90   $6.90  
  Purchase #6 $114.80   10.189%   $126.497   $126.50   $126.50   $126.50  
  Purchase #7 $55.99   13.669%   $63.6433   $63.64   $63.65   $63.60  
  7 purchase totals = $930.80       $1,024.6558   $1,024.66   $1,024.65   $1,024.60