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	$91.83	8.146%	$99.3105	$99.31	$99.30	$99.30
Purchase #2	$185.56	6.455%	$197.5379	$197.54	$197.55	$197.50
Purchase #3	$105.75	3.683%	$109.6448	$109.64	$109.65	$109.60
Purchase #4	$81.78	4.364%	$85.3489	$85.35	$85.35	$85.30
Purchase #5	$212.26	12.304%	$238.3765	$238.38	$238.40	$238.40
Purchase #6	$137.31	5.817%	$145.2973	$145.30	$145.30	$145.30
Purchase #7	$228.81	6.256%	$243.1244	$243.12	$243.10	$243.10
7 purchase totals =	$1,043.30		$1,118.6403	$1,118.64	$1,118.65	$1,118.50