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	$244.98	12.380%	$275.3085	$275.31	$275.30	$275.30
Purchase #2	$229.90	3.588%	$238.1488	$238.15	$238.15	$238.10
Purchase #3	$114.93	8.689%	$124.9163	$124.92	$124.90	$124.90
Purchase #4	$216.31	4.337%	$225.6914	$225.69	$225.70	$225.70
Purchase #5	$195.52	12.213%	$219.3989	$219.40	$219.40	$219.40
Purchase #6	$196.29	5.274%	$206.6423	$206.64	$206.65	$206.60
Purchase #7	$110.35	3.657%	$114.3855	$114.39	$114.40	$114.40
7 purchase totals =	$1,308.28		$1,404.4917	$1,404.50	$1,404.50	$1,404.40