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	$166.67	11.217%	$185.3654	$185.37	$185.35	$185.40
Purchase #2	$71.44	9.710%	$78.3768	$78.38	$78.40	$78.40
Purchase #3	$204.62	12.654%	$230.5126	$230.51	$230.50	$230.50
Purchase #4	$167.97	9.507%	$183.9389	$183.94	$183.95	$183.90
Purchase #5	$229.55	12.714%	$258.735	$258.74	$258.75	$258.70
Purchase #6	$150.52	10.645%	$166.5429	$166.54	$166.55	$166.50
Purchase #7	$133.43	13.746%	$151.7713	$151.77	$151.75	$151.80
7 purchase totals =	$1,124.20		$1,255.2429	$1,255.25	$1,255.25	$1,255.20