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 $92.37   4.237%   $96.2837   $96.28   $96.30   $96.30  
  Purchase #2 $8.28   12.337%   $9.3015   $9.30   $9.30   $9.30  
  Purchase #3 $173.57   4.621%   $181.5907   $181.59   $181.60   $181.60  
  Purchase #4 $225.88   13.862%   $257.1915   $257.19   $257.20   $257.20  
  Purchase #5 $21.99   3.215%   $22.697   $22.70   $22.70   $22.70  
  Purchase #6 $121.45   13.435%   $137.7668   $137.77   $137.75   $137.80  
  Purchase #7 $220.26   12.583%   $247.9753   $247.98   $248.00   $248.00  
  7 purchase totals = $863.80       $952.8065   $952.81   $952.85   $952.90