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	$123.57	6.654%	$131.7923	$131.79	$131.80	$131.80
Purchase #2	$139.70	3.625%	$144.7641	$144.76	$144.75	$144.80
Purchase #3	$50.39	11.297%	$56.0826	$56.08	$56.10	$56.10
Purchase #4	$157.98	4.625%	$165.2866	$165.29	$165.30	$165.30
Purchase #5	$20.98	3.251%	$21.6621	$21.66	$21.65	$21.70
Purchase #6	$152.89	4.756%	$160.1614	$160.16	$160.15	$160.20
Purchase #7	$205.34	8.380%	$222.5475	$222.55	$222.55	$222.50
7 purchase totals =	$850.85		$902.2966	$902.29	$902.30	$902.40