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	$206.91	5.512%	$218.3149	$218.31	$218.30	$218.30
Purchase #2	$162.96	10.111%	$179.4369	$179.44	$179.45	$179.40
Purchase #3	$146.55	7.835%	$158.0322	$158.03	$158.05	$158.00
Purchase #4	$49.75	5.251%	$52.3624	$52.36	$52.35	$52.40
Purchase #5	$100.40	6.123%	$106.5475	$106.55	$106.55	$106.50
Purchase #6	$131.78	3.360%	$136.2078	$136.21	$136.20	$136.20
Purchase #7	$56.65	4.142%	$58.9964	$59.00	$59.00	$59.00
7 purchase totals =	$855.00		$909.8981	$909.90	$909.90	$909.80