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	$167.77	11.666%	$187.342	$187.34	$187.35	$187.30
Purchase #2	$119.89	4.124%	$124.8343	$124.83	$124.85	$124.80
Purchase #3	$191.82	12.474%	$215.7476	$215.75	$215.75	$215.70
Purchase #4	$99.51	12.393%	$111.8423	$111.84	$111.85	$111.80
Purchase #5	$47.79	12.369%	$53.7011	$53.70	$53.70	$53.70
Purchase #6	$38.37	9.754%	$42.1126	$42.11	$42.10	$42.10
Purchase #7	$56.45	3.168%	$58.2383	$58.24	$58.25	$58.20
7 purchase totals =	$721.60		$793.8182	$793.81	$793.85	$793.60