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	$171.56	4.843%	$179.8687	$179.87	$179.85	$179.90
Purchase #2	$144.74	12.533%	$162.8803	$162.88	$162.90	$162.90
Purchase #3	$79.82	3.624%	$82.7127	$82.71	$82.70	$82.70
Purchase #4	$145.68	7.727%	$156.9367	$156.94	$156.95	$156.90
Purchase #5	$82.80	10.174%	$91.2241	$91.22	$91.20	$91.20
Purchase #6	$82.64	12.552%	$93.013	$93.01	$93.00	$93.00
Purchase #7	$237.46	8.704%	$258.1285	$258.13	$258.15	$258.10
7 purchase totals =	$944.70		$1,024.7640	$1,024.76	$1,024.75	$1,024.70