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	$38.56	10.655%	$42.6686	$42.67	$42.65	$42.70
Purchase #2	$106.57	7.362%	$114.4157	$114.42	$114.40	$114.40
Purchase #3	$88.35	11.664%	$98.6551	$98.66	$98.65	$98.70
Purchase #4	$115.99	9.711%	$127.2538	$127.25	$127.25	$127.30
Purchase #5	$112.88	13.453%	$128.0657	$128.07	$128.05	$128.10
Purchase #6	$219.96	9.291%	$240.3965	$240.40	$240.40	$240.40
Purchase #7	$67.57	5.558%	$71.3255	$71.33	$71.35	$71.30
7 purchase totals =	$749.88		$822.7809	$822.80	$822.75	$822.90