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	$79.90	11.516%	$89.1013	$89.10	$89.10	$89.10
Purchase #2	$146.54	6.559%	$156.1516	$156.15	$156.15	$156.20
Purchase #3	$75.54	4.285%	$78.7769	$78.78	$78.80	$78.80
Purchase #4	$143.33	10.194%	$157.9411	$157.94	$157.95	$157.90
Purchase #5	$212.59	11.166%	$236.3278	$236.33	$236.35	$236.30
Purchase #6	$92.43	6.472%	$98.4121	$98.41	$98.40	$98.40
Purchase #7	$234.46	10.450%	$258.9611	$258.96	$258.95	$259.00
7 purchase totals =	$984.79		$1,075.6719	$1,075.67	$1,075.70	$1,075.70