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	$147.29	12.808%	$166.1549	$166.15	$166.15	$166.20
Purchase #2	$142.59	6.233%	$151.4776	$151.48	$151.50	$151.50
Purchase #3	$41.66	9.844%	$45.761	$45.76	$45.75	$45.80
Purchase #4	$22.54	10.871%	$24.9903	$24.99	$25.00	$25.00
Purchase #5	$25.87	7.335%	$27.7676	$27.77	$27.75	$27.80
Purchase #6	$186.84	5.342%	$196.821	$196.82	$196.80	$196.80
Purchase #7	$87.38	4.454%	$91.2719	$91.27	$91.25	$91.30
7 purchase totals =	$654.17		$704.2443	$704.24	$704.20	$704.40