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	$28.31	9.582%	$31.0227	$31.02	$31.00	$31.00
Purchase #2	$67.55	12.229%	$75.8107	$75.81	$75.80	$75.80
Purchase #3	$184.29	3.335%	$190.4361	$190.44	$190.45	$190.40
Purchase #4	$138.79	9.403%	$151.8404	$151.84	$151.85	$151.80
Purchase #5	$58.34	7.393%	$62.6531	$62.65	$62.65	$62.70
Purchase #6	$164.57	12.815%	$185.6596	$185.66	$185.65	$185.70
Purchase #7	$81.39	11.266%	$90.5594	$90.56	$90.55	$90.60
7 purchase totals =	$723.24		$787.9820	$787.98	$787.95	$788.00