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	$48.87	4.630%	$51.1327	$51.13	$51.15	$51.10
Purchase #2	$115.80	6.802%	$123.6767	$123.68	$123.70	$123.70
Purchase #3	$188.45	12.794%	$212.5603	$212.56	$212.55	$212.60
Purchase #4	$225.58	8.556%	$244.8806	$244.88	$244.90	$244.90
Purchase #5	$243.60	6.279%	$258.8956	$258.90	$258.90	$258.90
Purchase #6	$91.76	5.278%	$96.6031	$96.60	$96.60	$96.60
Purchase #7	$106.63	4.121%	$111.0242	$111.02	$111.00	$111.00
7 purchase totals =	$1,020.69		$1,098.7732	$1,098.77	$1,098.80	$1,098.80