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	$183.50	7.255%	$196.8129	$196.81	$196.80	$196.80
Purchase #2	$91.76	12.384%	$103.1236	$103.12	$103.10	$103.10
Purchase #3	$46.25	11.357%	$51.5026	$51.50	$51.50	$51.50
Purchase #4	$10.91	4.446%	$11.3951	$11.40	$11.40	$11.40
Purchase #5	$136.86	3.376%	$141.4804	$141.48	$141.50	$141.50
Purchase #6	$190.30	7.590%	$204.7438	$204.74	$204.75	$204.70
Purchase #7	$134.39	10.703%	$148.7738	$148.77	$148.75	$148.80
7 purchase totals =	$793.97		$857.8322	$857.82	$857.80	$857.80