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	$105.48	6.125%	$111.9407	$111.94	$111.95	$111.90
Purchase #2	$234.80	6.668%	$250.4565	$250.46	$250.45	$250.50
Purchase #3	$58.65	7.327%	$62.9473	$62.95	$62.95	$62.90
Purchase #4	$81.67	13.656%	$92.8229	$92.82	$92.80	$92.80
Purchase #5	$228.96	7.457%	$246.0335	$246.03	$246.05	$246.00
Purchase #6	$16.38	11.104%	$18.1988	$18.20	$18.20	$18.20
Purchase #7	$52.31	13.725%	$59.4895	$59.49	$59.50	$59.50
7 purchase totals =	$778.25		$841.8892	$841.89	$841.90	$841.80