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	$147.34	3.295%	$152.1949	$152.19	$152.20	$152.20
Purchase #2	$124.83	11.439%	$139.1093	$139.11	$139.10	$139.10
Purchase #3	$102.32	12.170%	$114.7723	$114.77	$114.75	$114.80
Purchase #4	$200.85	7.495%	$215.9037	$215.90	$215.90	$215.90
Purchase #5	$91.83	7.840%	$99.0295	$99.03	$99.05	$99.00
Purchase #6	$95.28	5.194%	$100.2288	$100.23	$100.25	$100.20
Purchase #7	$13.88	13.309%	$15.7273	$15.73	$15.75	$15.70
7 purchase totals =	$776.33		$836.9658	$836.96	$837.00	$836.90