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	$117.87	5.582%	$124.4495	$124.45	$124.45	$124.40
Purchase #2	$115.33	3.820%	$119.7356	$119.74	$119.75	$119.70
Purchase #3	$83.41	7.819%	$89.9318	$89.93	$89.95	$89.90
Purchase #4	$51.32	7.749%	$55.2968	$55.30	$55.30	$55.30
Purchase #5	$210.85	12.533%	$237.2758	$237.28	$237.30	$237.30
Purchase #6	$125.64	4.670%	$131.5074	$131.51	$131.50	$131.50
Purchase #7	$49.87	4.682%	$52.2049	$52.20	$52.20	$52.20
7 purchase totals =	$754.29		$810.4018	$810.41	$810.45	$810.30