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	$18.39	6.201%	$19.5304	$19.53	$19.55	$19.50
Purchase #2	$78.39	4.400%	$81.8392	$81.84	$81.85	$81.80
Purchase #3	$155.39	8.594%	$168.7442	$168.74	$168.75	$168.70
Purchase #4	$72.36	8.764%	$78.7016	$78.70	$78.70	$78.70
Purchase #5	$108.78	4.131%	$113.2737	$113.27	$113.25	$113.30
Purchase #6	$111.83	10.828%	$123.939	$123.94	$123.95	$123.90
Purchase #7	$242.76	3.240%	$250.6254	$250.63	$250.65	$250.60
7 purchase totals =	$787.90		$836.6535	$836.65	$836.70	$836.50