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	$86.38	3.372%	$89.2927	$89.29	$89.30	$89.30
Purchase #2	$150.38	11.456%	$167.6075	$167.61	$167.60	$167.60
Purchase #3	$101.26	8.596%	$109.9643	$109.96	$109.95	$110.00
Purchase #4	$12.52	8.261%	$13.5543	$13.55	$13.55	$13.60
Purchase #5	$190.26	4.305%	$198.4507	$198.45	$198.45	$198.50
Purchase #6	$92.65	10.803%	$102.659	$102.66	$102.65	$102.70
Purchase #7	$84.64	4.405%	$88.3684	$88.37	$88.35	$88.40
7 purchase totals =	$718.09		$769.8969	$769.89	$769.85	$770.10