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	$99.89	12.769%	$112.645	$112.65	$112.65	$112.60
Purchase #2	$159.31	6.229%	$169.2334	$169.23	$169.25	$169.20
Purchase #3	$62.32	13.130%	$70.5026	$70.50	$70.50	$70.50
Purchase #4	$175.48	4.386%	$183.1766	$183.18	$183.20	$183.20
Purchase #5	$245.91	12.166%	$275.8274	$275.83	$275.85	$275.80
Purchase #6	$33.64	5.421%	$35.4636	$35.46	$35.45	$35.50
Purchase #7	$132.38	13.186%	$149.8356	$149.84	$149.85	$149.80
7 purchase totals =	$908.93		$996.6842	$996.69	$996.75	$996.60