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	$84.48	7.433%	$90.7594	$90.76	$90.75	$90.80
Purchase #2	$46.98	11.349%	$52.3118	$52.31	$52.30	$52.30
Purchase #3	$201.41	4.713%	$210.9025	$210.90	$210.90	$210.90
Purchase #4	$19.48	6.849%	$20.8142	$20.81	$20.80	$20.80
Purchase #5	$71.92	10.544%	$79.5032	$79.50	$79.50	$79.50
Purchase #6	$151.71	5.305%	$159.7582	$159.76	$159.75	$159.80
Purchase #7	$149.34	13.493%	$169.4904	$169.49	$169.50	$169.50
7 purchase totals =	$725.32		$783.5397	$783.53	$783.50	$783.60