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	$245.40	12.581%	$276.2738	$276.27	$276.25	$276.30
Purchase #2	$191.69	12.336%	$215.3369	$215.34	$215.35	$215.30
Purchase #3	$65.60	11.164%	$72.9236	$72.92	$72.90	$72.90
Purchase #4	$180.68	7.535%	$194.2942	$194.29	$194.30	$194.30
Purchase #5	$102.95	13.774%	$117.1303	$117.13	$117.15	$117.10
Purchase #6	$57.34	9.613%	$62.8521	$62.85	$62.85	$62.90
Purchase #7	$75.52	6.851%	$80.6939	$80.69	$80.70	$80.70
7 purchase totals =	$919.18		$1,019.5048	$1,019.49	$1,019.50	$1,019.50