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	$185.39	11.392%	$206.5096	$206.51	$206.50	$206.50
Purchase #2	$179.48	11.851%	$200.7502	$200.75	$200.75	$200.80
Purchase #3	$53.99	9.807%	$59.2848	$59.28	$59.30	$59.30
Purchase #4	$170.79	4.611%	$178.6651	$178.67	$178.65	$178.70
Purchase #5	$85.46	5.435%	$90.1048	$90.10	$90.10	$90.10
Purchase #6	$104.93	13.819%	$119.4303	$119.43	$119.45	$119.40
Purchase #7	$34.84	7.405%	$37.4199	$37.42	$37.40	$37.40
7 purchase totals =	$814.88		$892.1647	$892.16	$892.15	$892.20