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	$10.88	10.484%	$12.0207	$12.02	$12.00	$12.00
Purchase #2	$215.51	6.582%	$229.6949	$229.69	$229.70	$229.70
Purchase #3	$121.46	4.703%	$127.1723	$127.17	$127.15	$127.20
Purchase #4	$182.39	7.766%	$196.5544	$196.55	$196.55	$196.60
Purchase #5	$192.53	6.737%	$205.5007	$205.50	$205.50	$205.50
Purchase #6	$192.72	13.175%	$218.1109	$218.11	$218.10	$218.10
Purchase #7	$55.38	12.676%	$62.4	$62.40	$62.40	$62.40
7 purchase totals =	$970.87		$1,051.4539	$1,051.44	$1,051.40	$1,051.50