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 $126.86   6.346%   $134.9105   $134.91   $134.90   $134.90  
  Purchase #2 $87.77   10.416%   $96.9121   $96.91   $96.90   $96.90  
  Purchase #3 $227.88   6.537%   $242.7765   $242.78   $242.80   $242.80  
  Purchase #4 $5.64   11.267%   $6.2755   $6.28   $6.30   $6.30  
  Purchase #5 $187.65   5.859%   $198.6444   $198.64   $198.65   $198.60  
  Purchase #6 $182.39   13.120%   $206.3196   $206.32   $206.30   $206.30  
  Purchase #7 $169.41   3.179%   $174.7955   $174.80   $174.80   $174.80  
  7 purchase totals = $987.60       $1,060.6341   $1,060.64   $1,060.65   $1,060.60