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	$242.75	9.705%	$266.3089	$266.31	$266.30	$266.30
Purchase #2	$96.82	4.843%	$101.509	$101.51	$101.50	$101.50
Purchase #3	$138.76	4.181%	$144.5616	$144.56	$144.55	$144.60
Purchase #4	$227.46	8.850%	$247.5902	$247.59	$247.60	$247.60
Purchase #5	$64.44	10.353%	$71.1115	$71.11	$71.10	$71.10
Purchase #6	$101.56	6.216%	$107.873	$107.87	$107.85	$107.90
Purchase #7	$209.74	4.862%	$219.9376	$219.94	$219.95	$219.90
7 purchase totals =	$1,081.53		$1,158.8918	$1,158.89	$1,158.85	$1,158.90