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	$55.31	4.365%	$57.7243	$57.72	$57.70	$57.70
Purchase #2	$115.38	13.694%	$131.1801	$131.18	$131.20	$131.20
Purchase #3	$61.26	6.572%	$65.286	$65.29	$65.30	$65.30
Purchase #4	$115.88	13.533%	$131.562	$131.56	$131.55	$131.60
Purchase #5	$126.31	3.323%	$130.5073	$130.51	$130.50	$130.50
Purchase #6	$77.98	4.574%	$81.5468	$81.55	$81.55	$81.50
Purchase #7	$52.71	12.124%	$59.1006	$59.10	$59.10	$59.10
7 purchase totals =	$604.83		$656.9071	$656.91	$656.90	$656.90