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	$45.45	7.550%	$48.8815	$48.88	$48.90	$48.90
Purchase #2	$84.44	4.670%	$88.3833	$88.38	$88.40	$88.40
Purchase #3	$64.66	9.464%	$70.7794	$70.78	$70.80	$70.80
Purchase #4	$162.93	5.136%	$171.2981	$171.30	$171.30	$171.30
Purchase #5	$90.43	11.820%	$101.1188	$101.12	$101.10	$101.10
Purchase #6	$150.86	5.873%	$159.72	$159.72	$159.70	$159.70
Purchase #7	$203.56	9.776%	$223.46	$223.46	$223.45	$223.50
7 purchase totals =	$802.33		$863.6411	$863.64	$863.65	$863.70