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	$223.30	3.172%	$230.3831	$230.38	$230.40	$230.40
Purchase #2	$37.53	5.119%	$39.4512	$39.45	$39.45	$39.50
Purchase #3	$204.55	3.304%	$211.3083	$211.31	$211.30	$211.30
Purchase #4	$128.57	10.645%	$142.2563	$142.26	$142.25	$142.30
Purchase #5	$106.54	7.264%	$114.2791	$114.28	$114.30	$114.30
Purchase #6	$45.64	5.242%	$48.0324	$48.03	$48.05	$48.00
Purchase #7	$38.26	5.354%	$40.3084	$40.31	$40.30	$40.30
7 purchase totals =	$784.39		$826.0188	$826.02	$826.05	$826.10