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	$248.63	9.388%	$271.9714	$271.97	$271.95	$272.00
Purchase #2	$237.35	4.779%	$248.693	$248.69	$248.70	$248.70
Purchase #3	$45.31	12.663%	$51.0476	$51.05	$51.05	$51.00
Purchase #4	$40.29	4.652%	$42.1643	$42.16	$42.15	$42.20
Purchase #5	$209.32	9.285%	$228.7554	$228.76	$228.75	$228.80
Purchase #6	$79.87	13.281%	$90.4775	$90.48	$90.50	$90.50
Purchase #7	$113.44	12.696%	$127.8423	$127.84	$127.85	$127.80
7 purchase totals =	$974.21		$1,060.9515	$1,060.95	$1,060.95	$1,061.00