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	$246.57	3.781%	$255.8928	$255.89	$255.90	$255.90
Purchase #2	$146.53	3.263%	$151.3113	$151.31	$151.30	$151.30
Purchase #3	$155.53	8.858%	$169.3068	$169.31	$169.30	$169.30
Purchase #4	$41.64	3.765%	$43.2077	$43.21	$43.20	$43.20
Purchase #5	$226.28	12.466%	$254.4881	$254.49	$254.50	$254.50
Purchase #6	$202.53	8.113%	$218.9613	$218.96	$218.95	$219.00
Purchase #7	$200.64	9.222%	$219.143	$219.14	$219.15	$219.10
7 purchase totals =	$1,219.72		$1,312.3110	$1,312.31	$1,312.30	$1,312.30