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	$57.27	6.832%	$61.1827	$61.18	$61.20	$61.20
Purchase #2	$127.75	4.570%	$133.5882	$133.59	$133.60	$133.60
Purchase #3	$119.90	6.682%	$127.9117	$127.91	$127.90	$127.90
Purchase #4	$114.56	13.688%	$130.241	$130.24	$130.25	$130.20
Purchase #5	$161.30	4.434%	$168.452	$168.45	$168.45	$168.50
Purchase #6	$247.28	10.410%	$273.0218	$273.02	$273.00	$273.00
Purchase #7	$9.66	3.515%	$9.9995	$10.00	$10.00	$10.00
7 purchase totals =	$837.72		$904.3969	$904.39	$904.40	$904.40