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	$130.83	12.784%	$147.5553	$147.56	$147.55	$147.60
Purchase #2	$92.72	13.579%	$105.3104	$105.31	$105.30	$105.30
Purchase #3	$127.69	13.345%	$144.7302	$144.73	$144.75	$144.70
Purchase #4	$169.57	9.310%	$185.357	$185.36	$185.35	$185.40
Purchase #5	$188.81	9.215%	$206.2088	$206.21	$206.20	$206.20
Purchase #6	$74.63	5.641%	$78.8399	$78.84	$78.85	$78.80
Purchase #7	$45.70	7.133%	$48.9598	$48.96	$48.95	$49.00
7 purchase totals =	$829.95		$916.9614	$916.97	$916.95	$917.00