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	$98.31	12.405%	$110.5054	$110.51	$110.50	$110.50
Purchase #2	$219.64	4.842%	$230.275	$230.28	$230.30	$230.30
Purchase #3	$54.94	7.856%	$59.2561	$59.26	$59.25	$59.30
Purchase #4	$67.36	9.311%	$73.6319	$73.63	$73.65	$73.60
Purchase #5	$43.65	13.287%	$49.4498	$49.45	$49.45	$49.40
Purchase #6	$173.51	9.172%	$189.4243	$189.42	$189.40	$189.40
Purchase #7	$166.48	3.705%	$172.6481	$172.65	$172.65	$172.60
7 purchase totals =	$823.89		$885.1906	$885.20	$885.20	$885.10