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	$38.36	7.528%	$41.2477	$41.25	$41.25	$41.20
Purchase #2	$148.80	11.841%	$166.4194	$166.42	$166.40	$166.40
Purchase #3	$40.63	3.715%	$42.1394	$42.14	$42.15	$42.10
Purchase #4	$80.95	11.144%	$89.9711	$89.97	$89.95	$90.00
Purchase #5	$44.99	12.290%	$50.5193	$50.52	$50.50	$50.50
Purchase #6	$101.31	10.121%	$111.5636	$111.56	$111.55	$111.60
Purchase #7	$88.82	7.538%	$95.5153	$95.52	$95.50	$95.50
7 purchase totals =	$543.86		$597.3758	$597.38	$597.30	$597.30