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	$88.36	13.692%	$100.4583	$100.46	$100.45	$100.50
Purchase #2	$130.33	11.868%	$145.7976	$145.80	$145.80	$145.80
Purchase #3	$34.52	8.299%	$37.3848	$37.38	$37.40	$37.40
Purchase #4	$83.42	3.657%	$86.4707	$86.47	$86.45	$86.50
Purchase #5	$76.93	11.809%	$86.0147	$86.01	$86.00	$86.00
Purchase #6	$168.95	8.563%	$183.4172	$183.42	$183.40	$183.40
Purchase #7	$168.28	7.140%	$180.2952	$180.30	$180.30	$180.30
7 purchase totals =	$750.79		$819.8385	$819.84	$819.80	$819.90