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	$160.28	6.687%	$170.9979	$171.00	$171.00	$171.00
Purchase #2	$142.33	6.355%	$151.3751	$151.38	$151.40	$151.40
Purchase #3	$74.83	5.469%	$78.9225	$78.92	$78.90	$78.90
Purchase #4	$82.66	10.362%	$91.2252	$91.23	$91.25	$91.20
Purchase #5	$94.92	11.154%	$105.5074	$105.51	$105.50	$105.50
Purchase #6	$245.45	8.843%	$267.1551	$267.16	$267.15	$267.20
Purchase #7	$247.77	3.477%	$256.385	$256.39	$256.40	$256.40
7 purchase totals =	$1,048.24		$1,121.5682	$1,121.59	$1,121.60	$1,121.60