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	$159.49	6.622%	$170.0514	$170.05	$170.05	$170.10
Purchase #2	$39.63	3.312%	$40.9425	$40.94	$40.95	$40.90
Purchase #3	$168.66	8.661%	$183.2676	$183.27	$183.25	$183.30
Purchase #4	$212.96	13.873%	$242.5039	$242.50	$242.50	$242.50
Purchase #5	$134.30	12.853%	$151.5616	$151.56	$151.55	$151.60
Purchase #6	$53.32	4.642%	$55.7951	$55.80	$55.80	$55.80
Purchase #7	$161.80	12.146%	$181.4522	$181.45	$181.45	$181.50
7 purchase totals =	$930.16		$1,025.5743	$1,025.57	$1,025.55	$1,025.70