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	$234.88	8.191%	$254.119	$254.12	$254.10	$254.10
Purchase #2	$62.50	3.564%	$64.7275	$64.73	$64.75	$64.70
Purchase #3	$117.27	9.378%	$128.2676	$128.27	$128.25	$128.30
Purchase #4	$172.59	13.789%	$196.3884	$196.39	$196.40	$196.40
Purchase #5	$231.78	6.611%	$247.103	$247.10	$247.10	$247.10
Purchase #6	$244.76	9.288%	$267.4933	$267.49	$267.50	$267.50
Purchase #7	$88.87	12.421%	$99.9085	$99.91	$99.90	$99.90
7 purchase totals =	$1,152.65		$1,258.0073	$1,258.01	$1,258.00	$1,258.00