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	$91.35	9.426%	$99.9607	$99.96	$99.95	$100.00
Purchase #2	$163.36	9.825%	$179.4101	$179.41	$179.40	$179.40
Purchase #3	$175.53	9.119%	$191.5366	$191.54	$191.55	$191.50
Purchase #4	$9.28	10.800%	$10.2822	$10.28	$10.30	$10.30
Purchase #5	$189.57	8.645%	$205.9583	$205.96	$205.95	$206.00
Purchase #6	$204.39	3.261%	$211.0552	$211.06	$211.05	$211.10
Purchase #7	$209.37	9.681%	$229.6391	$229.64	$229.65	$229.60
7 purchase totals =	$1,042.85		$1,127.8422	$1,127.85	$1,127.85	$1,127.90