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	$35.75	3.854%	$37.1278	$37.13	$37.15	$37.10
Purchase #2	$156.54	6.400%	$166.5586	$166.56	$166.55	$166.60
Purchase #3	$181.56	6.747%	$193.8099	$193.81	$193.80	$193.80
Purchase #4	$175.77	5.295%	$185.077	$185.08	$185.10	$185.10
Purchase #5	$203.99	9.671%	$223.7179	$223.72	$223.70	$223.70
Purchase #6	$125.33	12.204%	$140.6253	$140.63	$140.65	$140.60
Purchase #7	$177.53	10.745%	$196.6056	$196.61	$196.60	$196.60
7 purchase totals =	$1,056.47		$1,143.5221	$1,143.54	$1,143.55	$1,143.50