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	$122.63	4.291%	$127.8921	$127.89	$127.90	$127.90
Purchase #2	$79.93	12.504%	$89.9244	$89.92	$89.90	$89.90
Purchase #3	$14.85	4.833%	$15.5677	$15.57	$15.55	$15.60
Purchase #4	$76.85	10.753%	$85.1137	$85.11	$85.10	$85.10
Purchase #5	$50.45	7.362%	$54.1641	$54.16	$54.15	$54.20
Purchase #6	$227.55	7.164%	$243.8517	$243.85	$243.85	$243.90
Purchase #7	$39.87	4.154%	$41.5262	$41.53	$41.55	$41.50
7 purchase totals =	$612.13		$658.0399	$658.03	$658.00	$658.10