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	$56.83	5.425%	$59.913	$59.91	$59.90	$59.90
Purchase #2	$165.79	10.235%	$182.7586	$182.76	$182.75	$182.80
Purchase #3	$209.90	6.840%	$224.2572	$224.26	$224.25	$224.30
Purchase #4	$204.90	8.370%	$222.0501	$222.05	$222.05	$222.10
Purchase #5	$38.68	10.688%	$42.8141	$42.81	$42.80	$42.80
Purchase #6	$108.71	6.151%	$115.3968	$115.40	$115.40	$115.40
Purchase #7	$209.51	13.260%	$237.291	$237.29	$237.30	$237.30
7 purchase totals =	$994.32		$1,084.4808	$1,084.48	$1,084.45	$1,084.60