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	$153.31	8.133%	$165.7787	$165.78	$165.80	$165.80
Purchase #2	$55.40	10.301%	$61.1068	$61.11	$61.10	$61.10
Purchase #3	$46.99	7.402%	$50.4682	$50.47	$50.45	$50.50
Purchase #4	$204.54	7.270%	$219.4101	$219.41	$219.40	$219.40
Purchase #5	$130.41	7.307%	$139.9391	$139.94	$139.95	$139.90
Purchase #6	$198.34	12.332%	$222.7993	$222.80	$222.80	$222.80
Purchase #7	$186.62	9.576%	$204.4907	$204.49	$204.50	$204.50
7 purchase totals =	$975.61		$1,063.9929	$1,064.00	$1,064.00	$1,064.00