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	$219.58	3.862%	$228.0602	$228.06	$228.05	$228.10
Purchase #2	$123.58	8.598%	$134.2054	$134.21	$134.20	$134.20
Purchase #3	$116.81	9.807%	$128.2656	$128.27	$128.25	$128.30
Purchase #4	$42.92	6.530%	$45.7227	$45.72	$45.70	$45.70
Purchase #5	$75.70	9.320%	$82.7552	$82.76	$82.75	$82.80
Purchase #6	$73.32	7.599%	$78.8916	$78.89	$78.90	$78.90
Purchase #7	$126.63	13.768%	$144.0644	$144.06	$144.05	$144.10
7 purchase totals =	$778.54		$841.9651	$841.97	$841.90	$842.10