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	$190.50	10.556%	$210.6092	$210.61	$210.60	$210.60
Purchase #2	$70.33	11.227%	$78.2259	$78.23	$78.25	$78.20
Purchase #3	$208.31	8.858%	$226.7621	$226.76	$226.75	$226.80
Purchase #4	$239.59	3.821%	$248.7447	$248.74	$248.75	$248.70
Purchase #5	$238.34	13.349%	$270.156	$270.16	$270.15	$270.20
Purchase #6	$21.93	4.271%	$22.8666	$22.87	$22.85	$22.90
Purchase #7	$85.60	5.283%	$90.1222	$90.12	$90.10	$90.10
7 purchase totals =	$1,054.60		$1,147.4867	$1,147.49	$1,147.45	$1,147.50