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	$154.72	13.177%	$175.1075	$175.11	$175.10	$175.10
Purchase #2	$84.56	6.614%	$90.1528	$90.15	$90.15	$90.20
Purchase #3	$218.89	8.857%	$238.2771	$238.28	$238.30	$238.30
Purchase #4	$168.55	5.812%	$178.3461	$178.35	$178.35	$178.30
Purchase #5	$176.78	12.433%	$198.7591	$198.76	$198.75	$198.80
Purchase #6	$25.64	9.656%	$28.1158	$28.12	$28.10	$28.10
Purchase #7	$92.91	6.620%	$99.0606	$99.06	$99.05	$99.10
7 purchase totals =	$922.05		$1,007.8190	$1,007.83	$1,007.80	$1,007.90