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	$73.31	6.269%	$77.9058	$77.91	$77.90	$77.90
Purchase #2	$102.56	8.305%	$111.0776	$111.08	$111.10	$111.10
Purchase #3	$139.29	8.122%	$150.6031	$150.60	$150.60	$150.60
Purchase #4	$61.79	9.823%	$67.8596	$67.86	$67.85	$67.90
Purchase #5	$125.81	13.534%	$142.8371	$142.84	$142.85	$142.80
Purchase #6	$188.41	9.558%	$206.4182	$206.42	$206.40	$206.40
Purchase #7	$167.85	4.397%	$175.2304	$175.23	$175.25	$175.20
7 purchase totals =	$859.02		$931.9318	$931.94	$931.95	$931.90