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	$31.31	7.270%	$33.5862	$33.59	$33.60	$33.60
Purchase #2	$48.91	12.221%	$54.8873	$54.89	$54.90	$54.90
Purchase #3	$118.71	6.241%	$126.1187	$126.12	$126.10	$126.10
Purchase #4	$121.43	12.657%	$136.7994	$136.80	$136.80	$136.80
Purchase #5	$179.44	6.521%	$191.1413	$191.14	$191.15	$191.10
Purchase #6	$101.79	13.397%	$115.4268	$115.43	$115.45	$115.40
Purchase #7	$149.66	12.680%	$168.6369	$168.64	$168.65	$168.60
7 purchase totals =	$751.25		$826.5966	$826.61	$826.65	$826.50