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 $241.31   4.553%   $252.2968   $252.30   $252.30   $252.30  
  Purchase #2 $95.76   3.609%   $99.216   $99.22   $99.20   $99.20  
  Purchase #3 $25.26   7.610%   $27.1823   $27.18   $27.20   $27.20  
  Purchase #4 $172.67   3.564%   $178.824   $178.82   $178.80   $178.80  
  Purchase #5 $86.70   11.425%   $96.6055   $96.61   $96.60   $96.60  
  Purchase #6 $210.89   4.114%   $219.566   $219.57   $219.55   $219.60  
  Purchase #7 $91.95   6.852%   $98.2504   $98.25   $98.25   $98.30  
  7 purchase totals = $924.54       $971.9410   $971.95   $971.90   $972.00