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	$51.65	3.206%	$53.3059	$53.31	$53.30	$53.30
Purchase #2	$147.53	6.343%	$156.8878	$156.89	$156.90	$156.90
Purchase #3	$202.90	9.131%	$221.4268	$221.43	$221.45	$221.40
Purchase #4	$170.25	7.570%	$183.1379	$183.14	$183.15	$183.10
Purchase #5	$78.64	13.705%	$89.4176	$89.42	$89.40	$89.40
Purchase #6	$38.40	7.324%	$41.2124	$41.21	$41.20	$41.20
Purchase #7	$174.86	11.456%	$194.892	$194.89	$194.90	$194.90
7 purchase totals =	$864.23		$940.2804	$940.29	$940.30	$940.20