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	$152.71	4.572%	$159.6919	$159.69	$159.70	$159.70
Purchase #2	$170.60	11.857%	$190.828	$190.83	$190.85	$190.80
Purchase #3	$167.65	4.669%	$175.4776	$175.48	$175.50	$175.50
Purchase #4	$172.80	4.288%	$180.2097	$180.21	$180.20	$180.20
Purchase #5	$39.72	3.304%	$41.0323	$41.03	$41.05	$41.00
Purchase #6	$95.81	3.114%	$98.7935	$98.79	$98.80	$98.80
Purchase #7	$75.69	3.850%	$78.6041	$78.60	$78.60	$78.60
7 purchase totals =	$874.98		$924.6371	$924.63	$924.70	$924.60