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	$232.99	6.462%	$248.0458	$248.05	$248.05	$248.00
Purchase #2	$158.56	6.445%	$168.7792	$168.78	$168.80	$168.80
Purchase #3	$229.29	4.655%	$239.9634	$239.96	$239.95	$240.00
Purchase #4	$72.97	12.790%	$82.3029	$82.30	$82.30	$82.30
Purchase #5	$131.30	7.763%	$141.4928	$141.49	$141.50	$141.50
Purchase #6	$58.62	4.490%	$61.252	$61.25	$61.25	$61.30
Purchase #7	$95.98	3.622%	$99.4564	$99.46	$99.45	$99.50
7 purchase totals =	$979.71		$1,041.2925	$1,041.29	$1,041.30	$1,041.40