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	$104.58	11.403%	$116.5053	$116.51	$116.50	$116.50
Purchase #2	$148.38	5.358%	$156.3302	$156.33	$156.35	$156.30
Purchase #3	$84.88	4.294%	$88.5247	$88.52	$88.50	$88.50
Purchase #4	$174.46	12.783%	$196.7612	$196.76	$196.75	$196.80
Purchase #5	$243.73	4.608%	$254.9611	$254.96	$254.95	$255.00
Purchase #6	$236.75	6.718%	$252.6549	$252.65	$252.65	$252.70
Purchase #7	$58.82	11.616%	$65.6525	$65.65	$65.65	$65.70
7 purchase totals =	$1,051.60		$1,131.3899	$1,131.38	$1,131.35	$1,131.50