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	$206.30	8.340%	$223.5054	$223.51	$223.50	$223.50
Purchase #2	$164.58	6.550%	$175.36	$175.36	$175.35	$175.40
Purchase #3	$111.32	9.759%	$122.1837	$122.18	$122.20	$122.20
Purchase #4	$33.50	12.793%	$37.7857	$37.79	$37.80	$37.80
Purchase #5	$89.54	11.479%	$99.8183	$99.82	$99.80	$99.80
Purchase #6	$105.75	7.219%	$113.3841	$113.38	$113.40	$113.40
Purchase #7	$183.39	9.372%	$200.5773	$200.58	$200.60	$200.60
7 purchase totals =	$894.38		$972.6145	$972.62	$972.65	$972.70