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	$173.54	10.702%	$192.1123	$192.11	$192.10	$192.10
Purchase #2	$122.32	7.681%	$131.7154	$131.72	$131.70	$131.70
Purchase #3	$151.56	10.423%	$167.3571	$167.36	$167.35	$167.40
Purchase #4	$61.44	4.243%	$64.0469	$64.05	$64.05	$64.00
Purchase #5	$26.84	3.225%	$27.7056	$27.71	$27.70	$27.70
Purchase #6	$25.47	13.131%	$28.8145	$28.81	$28.80	$28.80
Purchase #7	$48.47	10.485%	$53.5521	$53.55	$53.55	$53.60
7 purchase totals =	$609.64		$665.3039	$665.31	$665.25	$665.30