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	$247.42	12.140%	$277.4568	$277.46	$277.45	$277.50
Purchase #2	$166.58	9.402%	$182.2419	$182.24	$182.25	$182.20
Purchase #3	$162.31	4.782%	$170.0717	$170.07	$170.05	$170.10
Purchase #4	$143.88	6.222%	$152.8322	$152.83	$152.85	$152.80
Purchase #5	$189.83	11.610%	$211.8693	$211.87	$211.85	$211.90
Purchase #6	$153.76	11.177%	$170.9458	$170.95	$170.95	$170.90
Purchase #7	$98.78	11.267%	$109.9095	$109.91	$109.90	$109.90
7 purchase totals =	$1,162.56		$1,275.3272	$1,275.33	$1,275.30	$1,275.30