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	$47.51	6.156%	$50.4347	$50.43	$50.45	$50.40
Purchase #2	$225.27	5.854%	$238.4573	$238.46	$238.45	$238.50
Purchase #3	$250.97	9.582%	$275.0179	$275.02	$275.00	$275.00
Purchase #4	$115.69	13.401%	$131.1936	$131.19	$131.20	$131.20
Purchase #5	$120.38	3.601%	$124.7149	$124.71	$124.70	$124.70
Purchase #6	$42.61	7.263%	$45.7048	$45.70	$45.70	$45.70
Purchase #7	$81.54	9.327%	$89.1452	$89.15	$89.15	$89.10
7 purchase totals =	$883.97		$954.6684	$954.66	$954.65	$954.60