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	$84.75	6.780%	$90.4961	$90.50	$90.50	$90.50
Purchase #2	$6.80	13.705%	$7.7319	$7.73	$7.75	$7.70
Purchase #3	$53.74	3.399%	$55.5666	$55.57	$55.55	$55.60
Purchase #4	$29.52	3.444%	$30.5367	$30.54	$30.55	$30.50
Purchase #5	$131.59	4.200%	$137.1168	$137.12	$137.10	$137.10
Purchase #6	$246.73	10.366%	$272.306	$272.31	$272.30	$272.30
Purchase #7	$63.57	12.649%	$71.611	$71.61	$71.60	$71.60
7 purchase totals =	$616.70		$665.3651	$665.38	$665.35	$665.30