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	$132.75	7.341%	$142.4952	$142.50	$142.50	$142.50
Purchase #2	$166.56	13.544%	$189.1189	$189.12	$189.10	$189.10
Purchase #3	$173.94	10.468%	$192.148	$192.15	$192.15	$192.10
Purchase #4	$138.30	6.125%	$146.7709	$146.77	$146.75	$146.80
Purchase #5	$127.34	3.846%	$132.2375	$132.24	$132.25	$132.20
Purchase #6	$240.86	9.818%	$264.5076	$264.51	$264.50	$264.50
Purchase #7	$80.43	10.164%	$88.6049	$88.60	$88.60	$88.60
7 purchase totals =	$1,060.18		$1,155.8830	$1,155.89	$1,155.85	$1,155.80