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	$156.37	6.523%	$166.57	$166.57	$166.55	$166.60
Purchase #2	$247.47	6.449%	$263.4293	$263.43	$263.45	$263.40
Purchase #3	$108.73	8.773%	$118.2689	$118.27	$118.25	$118.30
Purchase #4	$177.37	4.539%	$185.4208	$185.42	$185.40	$185.40
Purchase #5	$38.87	4.144%	$40.4808	$40.48	$40.50	$40.50
Purchase #6	$202.76	10.419%	$223.8856	$223.89	$223.90	$223.90
Purchase #7	$98.58	12.360%	$110.7645	$110.76	$110.75	$110.80
7 purchase totals =	$1,030.15		$1,108.8199	$1,108.82	$1,108.80	$1,108.90