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	$52.47	3.419%	$54.2639	$54.26	$54.25	$54.30
Purchase #2	$164.50	9.195%	$179.6258	$179.63	$179.65	$179.60
Purchase #3	$158.68	9.765%	$174.1751	$174.18	$174.20	$174.20
Purchase #4	$91.72	3.685%	$95.0999	$95.10	$95.10	$95.10
Purchase #5	$53.51	9.250%	$58.4597	$58.46	$58.45	$58.50
Purchase #6	$206.80	13.124%	$233.9404	$233.94	$233.95	$233.90
Purchase #7	$42.31	3.437%	$43.7642	$43.76	$43.75	$43.80
7 purchase totals =	$769.99		$839.3290	$839.33	$839.35	$839.40