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	$92.83	7.835%	$100.1032	$100.10	$100.10	$100.10
Purchase #2	$232.49	9.481%	$254.5324	$254.53	$254.55	$254.50
Purchase #3	$140.78	9.579%	$154.2653	$154.27	$154.25	$154.30
Purchase #4	$129.47	11.312%	$144.1156	$144.12	$144.10	$144.10
Purchase #5	$178.61	3.404%	$184.6899	$184.69	$184.70	$184.70
Purchase #6	$93.36	6.670%	$99.5871	$99.59	$99.60	$99.60
Purchase #7	$7.96	7.769%	$8.5784	$8.58	$8.60	$8.60
7 purchase totals =	$875.50		$945.8719	$945.88	$945.90	$945.90