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	$44.96	12.581%	$50.6164	$50.62	$50.60	$50.60
Purchase #2	$56.69	5.736%	$59.9417	$59.94	$59.95	$59.90
Purchase #3	$172.86	5.148%	$181.7588	$181.76	$181.75	$181.80
Purchase #4	$82.41	12.610%	$92.8019	$92.80	$92.80	$92.80
Purchase #5	$74.53	8.164%	$80.6146	$80.61	$80.60	$80.60
Purchase #6	$142.60	9.267%	$155.8147	$155.81	$155.80	$155.80
Purchase #7	$72.55	13.541%	$82.374	$82.37	$82.35	$82.40
7 purchase totals =	$646.60		$703.9221	$703.91	$703.85	$703.90