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	$55.36	10.492%	$61.1684	$61.17	$61.15	$61.20
Purchase #2	$36.95	12.855%	$41.6999	$41.70	$41.70	$41.70
Purchase #3	$65.90	13.443%	$74.7589	$74.76	$74.75	$74.80
Purchase #4	$73.52	12.266%	$82.538	$82.54	$82.55	$82.50
Purchase #5	$219.78	9.450%	$240.5492	$240.55	$240.55	$240.50
Purchase #6	$160.77	3.334%	$166.1301	$166.13	$166.15	$166.10
Purchase #7	$6.83	6.458%	$7.2711	$7.27	$7.25	$7.30
7 purchase totals =	$619.11		$674.1156	$674.12	$674.10	$674.10