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	$28.37	7.803%	$30.5837	$30.58	$30.60	$30.60
Purchase #2	$142.54	10.869%	$158.0327	$158.03	$158.05	$158.00
Purchase #3	$160.35	13.719%	$182.3484	$182.35	$182.35	$182.30
Purchase #4	$233.79	3.692%	$242.4215	$242.42	$242.40	$242.40
Purchase #5	$233.77	3.457%	$241.8514	$241.85	$241.85	$241.90
Purchase #6	$98.87	10.410%	$109.1624	$109.16	$109.15	$109.20
Purchase #7	$75.89	13.806%	$86.3674	$86.37	$86.35	$86.40
7 purchase totals =	$973.58		$1,050.7675	$1,050.76	$1,050.75	$1,050.80