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	$18.60	12.104%	$20.8513	$20.85	$20.85	$20.90
Purchase #2	$82.87	7.763%	$89.3032	$89.30	$89.30	$89.30
Purchase #3	$171.27	11.609%	$191.1527	$191.15	$191.15	$191.20
Purchase #4	$23.67	7.315%	$25.4015	$25.40	$25.40	$25.40
Purchase #5	$102.26	8.115%	$110.5584	$110.56	$110.55	$110.60
Purchase #6	$52.28	3.719%	$54.2243	$54.22	$54.20	$54.20
Purchase #7	$172.63	13.683%	$196.251	$196.25	$196.25	$196.30
7 purchase totals =	$623.58		$687.7424	$687.73	$687.70	$687.90