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	$155.54	10.406%	$171.7255	$171.73	$171.75	$171.70
Purchase #2	$143.29	4.185%	$149.2867	$149.29	$149.30	$149.30
Purchase #3	$69.99	4.119%	$72.8729	$72.87	$72.85	$72.90
Purchase #4	$193.65	6.522%	$206.2799	$206.28	$206.30	$206.30
Purchase #5	$152.48	9.419%	$166.8421	$166.84	$166.85	$166.80
Purchase #6	$238.90	4.862%	$250.5153	$250.52	$250.50	$250.50
Purchase #7	$37.55	7.405%	$40.3306	$40.33	$40.35	$40.30
7 purchase totals =	$991.40		$1,057.8530	$1,057.86	$1,057.90	$1,057.80