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	$89.84	3.272%	$92.7796	$92.78	$92.80	$92.80
Purchase #2	$54.75	13.564%	$62.1763	$62.18	$62.20	$62.20
Purchase #3	$202.65	7.547%	$217.944	$217.94	$217.95	$217.90
Purchase #4	$54.88	11.470%	$61.1747	$61.17	$61.15	$61.20
Purchase #5	$163.65	13.152%	$185.1732	$185.17	$185.15	$185.20
Purchase #6	$120.29	9.503%	$131.7212	$131.72	$131.70	$131.70
Purchase #7	$19.37	4.377%	$20.2178	$20.22	$20.20	$20.20
7 purchase totals =	$705.43		$771.1868	$771.18	$771.15	$771.20