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	$80.46	11.398%	$89.6308	$89.63	$89.65	$89.60
Purchase #2	$129.75	3.152%	$133.8397	$133.84	$133.85	$133.80
Purchase #3	$46.53	3.695%	$48.2493	$48.25	$48.25	$48.20
Purchase #4	$165.89	9.663%	$181.92	$181.92	$181.90	$181.90
Purchase #5	$20.69	5.400%	$21.8073	$21.81	$21.80	$21.80
Purchase #6	$97.80	4.263%	$101.9692	$101.97	$101.95	$102.00
Purchase #7	$62.36	13.677%	$70.889	$70.89	$70.90	$70.90
7 purchase totals =	$603.48		$648.3053	$648.31	$648.30	$648.20