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 $249.71   6.412%   $265.7214   $265.72   $265.70   $265.70  
  Purchase #2 $95.46   3.420%   $98.7247   $98.72   $98.70   $98.70  
  Purchase #3 $240.77   7.545%   $258.9361   $258.94   $258.95   $258.90  
  Purchase #4 $149.90   10.621%   $165.8209   $165.82   $165.80   $165.80  
  Purchase #5 $249.41   6.801%   $266.3724   $266.37   $266.35   $266.40  
  Purchase #6 $61.91   9.544%   $67.8187   $67.82   $67.80   $67.80  
  Purchase #7 $44.99   5.239%   $47.347   $47.35   $47.35   $47.30  
  7 purchase totals = $1,092.15       $1,170.7412   $1,170.74   $1,170.65   $1,170.60