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	$108.25	7.576%	$116.451	$116.45	$116.45	$116.50
Purchase #2	$243.46	10.484%	$268.9843	$268.98	$269.00	$269.00
Purchase #3	$82.86	10.427%	$91.4998	$91.50	$91.50	$91.50
Purchase #4	$71.77	9.538%	$78.6154	$78.62	$78.60	$78.60
Purchase #5	$165.45	8.264%	$179.1228	$179.12	$179.10	$179.10
Purchase #6	$78.27	4.679%	$81.9323	$81.93	$81.95	$81.90
Purchase #7	$29.84	11.352%	$33.2274	$33.23	$33.25	$33.20
7 purchase totals =	$779.90		$849.8330	$849.83	$849.85	$849.80