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	$135.40	11.426%	$150.8708	$150.87	$150.85	$150.90
Purchase #2	$165.26	3.476%	$171.0044	$171.00	$171.00	$171.00
Purchase #3	$235.84	9.446%	$258.1174	$258.12	$258.10	$258.10
Purchase #4	$62.50	4.237%	$65.1481	$65.15	$65.15	$65.10
Purchase #5	$59.56	10.572%	$65.8567	$65.86	$65.85	$65.90
Purchase #6	$12.30	4.604%	$12.8663	$12.87	$12.85	$12.90
Purchase #7	$96.99	9.151%	$105.8656	$105.87	$105.85	$105.90
7 purchase totals =	$767.85		$829.7293	$829.74	$829.65	$829.80