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	$241.48	9.855%	$265.2779	$265.28	$265.30	$265.30
Purchase #2	$94.26	5.284%	$99.2407	$99.24	$99.25	$99.20
Purchase #3	$35.31	8.591%	$38.3435	$38.34	$38.35	$38.30
Purchase #4	$227.89	13.765%	$259.2591	$259.26	$259.25	$259.30
Purchase #5	$96.52	9.866%	$106.0427	$106.04	$106.05	$106.00
Purchase #6	$74.84	4.663%	$78.3298	$78.33	$78.35	$78.30
Purchase #7	$53.89	3.194%	$55.6112	$55.61	$55.60	$55.60
7 purchase totals =	$824.19		$902.1049	$902.10	$902.15	$902.00