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	$110.83	5.390%	$116.8037	$116.80	$116.80	$116.80
Purchase #2	$61.78	7.330%	$66.3085	$66.31	$66.30	$66.30
Purchase #3	$113.46	9.416%	$124.1434	$124.14	$124.15	$124.10
Purchase #4	$133.80	5.802%	$141.5631	$141.56	$141.55	$141.60
Purchase #5	$45.48	13.820%	$51.7653	$51.77	$51.75	$51.80
Purchase #6	$26.67	6.850%	$28.4969	$28.50	$28.50	$28.50
Purchase #7	$62.29	13.701%	$70.8244	$70.82	$70.80	$70.80
7 purchase totals =	$554.31		$599.9053	$599.90	$599.85	$599.90