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	$38.78	10.786%	$42.9628	$42.96	$42.95	$43.00
Purchase #2	$89.80	3.280%	$92.7454	$92.75	$92.75	$92.70
Purchase #3	$89.38	7.153%	$95.7734	$95.77	$95.75	$95.80
Purchase #4	$58.56	5.788%	$61.9495	$61.95	$61.95	$61.90
Purchase #5	$116.89	12.200%	$131.1506	$131.15	$131.15	$131.20
Purchase #6	$39.46	8.282%	$42.7281	$42.73	$42.75	$42.70
Purchase #7	$45.28	3.149%	$46.7059	$46.71	$46.70	$46.70
7 purchase totals =	$478.15		$514.0157	$514.02	$514.00	$514.00