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	$65.76	6.854%	$70.2672	$70.27	$70.25	$70.30
Purchase #2	$125.77	4.771%	$131.7705	$131.77	$131.75	$131.80
Purchase #3	$134.47	11.807%	$150.3469	$150.35	$150.35	$150.30
Purchase #4	$212.88	13.823%	$242.3064	$242.31	$242.30	$242.30
Purchase #5	$94.96	10.699%	$105.1198	$105.12	$105.10	$105.10
Purchase #6	$174.92	13.695%	$198.8753	$198.88	$198.90	$198.90
Purchase #7	$220.84	13.668%	$251.0244	$251.02	$251.00	$251.00
7 purchase totals =	$1,029.60		$1,149.7105	$1,149.72	$1,149.65	$1,149.70