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	$71.70	10.826%	$79.4622	$79.46	$79.45	$79.50
Purchase #2	$63.48	13.275%	$71.907	$71.91	$71.90	$71.90
Purchase #3	$86.33	5.205%	$90.8235	$90.82	$90.80	$90.80
Purchase #4	$154.48	11.619%	$172.429	$172.43	$172.45	$172.40
Purchase #5	$71.48	9.828%	$78.5051	$78.51	$78.50	$78.50
Purchase #6	$184.31	12.828%	$207.9533	$207.95	$207.95	$208.00
Purchase #7	$147.76	4.426%	$154.2999	$154.30	$154.30	$154.30
7 purchase totals =	$779.54		$855.3800	$855.38	$855.35	$855.40