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	$93.81	6.556%	$99.9602	$99.96	$99.95	$100.00
Purchase #2	$229.38	9.364%	$250.8591	$250.86	$250.85	$250.90
Purchase #3	$136.76	10.612%	$151.273	$151.27	$151.25	$151.30
Purchase #4	$96.40	13.866%	$109.7668	$109.77	$109.75	$109.80
Purchase #5	$172.56	4.317%	$180.0094	$180.01	$180.00	$180.00
Purchase #6	$232.50	7.374%	$249.6446	$249.64	$249.65	$249.60
Purchase #7	$111.73	11.112%	$124.1454	$124.15	$124.15	$124.10
7 purchase totals =	$1,073.14		$1,165.6585	$1,165.66	$1,165.60	$1,165.70