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	$247.41	6.815%	$264.271	$264.27	$264.25	$264.30
Purchase #2	$227.69	5.438%	$240.0718	$240.07	$240.05	$240.10
Purchase #3	$229.79	12.465%	$258.4333	$258.43	$258.45	$258.40
Purchase #4	$42.80	9.620%	$46.9174	$46.92	$46.90	$46.90
Purchase #5	$79.38	11.625%	$88.6079	$88.61	$88.60	$88.60
Purchase #6	$221.28	3.663%	$229.3855	$229.39	$229.40	$229.40
Purchase #7	$175.88	13.848%	$200.2359	$200.24	$200.25	$200.20
7 purchase totals =	$1,224.23		$1,327.9228	$1,327.93	$1,327.90	$1,327.90