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	$171.35	5.362%	$180.5378	$180.54	$180.55	$180.50
Purchase #2	$161.42	5.354%	$170.0624	$170.06	$170.05	$170.10
Purchase #3	$215.71	9.457%	$236.1097	$236.11	$236.10	$236.10
Purchase #4	$40.28	6.478%	$42.8893	$42.89	$42.90	$42.90
Purchase #5	$80.87	11.696%	$90.3286	$90.33	$90.35	$90.30
Purchase #6	$180.52	10.317%	$199.1442	$199.14	$199.15	$199.10
Purchase #7	$33.32	8.793%	$36.2498	$36.25	$36.25	$36.20
7 purchase totals =	$883.47		$955.3218	$955.32	$955.35	$955.20