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	$75.68	3.798%	$78.5543	$78.55	$78.55	$78.60
Purchase #2	$161.48	6.403%	$171.8196	$171.82	$171.80	$171.80
Purchase #3	$98.96	12.356%	$111.1875	$111.19	$111.20	$111.20
Purchase #4	$186.76	11.343%	$207.9442	$207.94	$207.95	$207.90
Purchase #5	$191.28	9.705%	$209.8437	$209.84	$209.85	$209.80
Purchase #6	$67.35	4.377%	$70.2979	$70.30	$70.30	$70.30
Purchase #7	$244.73	4.447%	$255.6131	$255.61	$255.60	$255.60
7 purchase totals =	$1,026.24		$1,105.2603	$1,105.25	$1,105.25	$1,105.20