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	$173.79	6.460%	$185.0168	$185.02	$185.00	$185.00
Purchase #2	$26.74	11.387%	$29.7849	$29.78	$29.80	$29.80
Purchase #3	$191.27	10.553%	$211.4547	$211.45	$211.45	$211.50
Purchase #4	$112.82	5.577%	$119.112	$119.11	$119.10	$119.10
Purchase #5	$37.34	7.830%	$40.2637	$40.26	$40.25	$40.30
Purchase #6	$226.34	10.564%	$250.2506	$250.25	$250.25	$250.30
Purchase #7	$244.52	7.366%	$262.5313	$262.53	$262.55	$262.50
7 purchase totals =	$1,012.82		$1,098.4140	$1,098.40	$1,098.40	$1,098.50