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	$207.35	7.657%	$223.2268	$223.23	$223.25	$223.20
Purchase #2	$168.84	6.276%	$179.4364	$179.44	$179.45	$179.40
Purchase #3	$91.36	9.576%	$100.1086	$100.11	$100.10	$100.10
Purchase #4	$38.57	12.671%	$43.4572	$43.46	$43.45	$43.50
Purchase #5	$154.91	13.419%	$175.6974	$175.70	$175.70	$175.70
Purchase #6	$250.26	8.264%	$270.9415	$270.94	$270.95	$270.90
Purchase #7	$35.41	13.734%	$40.2732	$40.27	$40.25	$40.30
7 purchase totals =	$946.70		$1,033.1411	$1,033.15	$1,033.15	$1,033.10