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	$184.61	8.607%	$200.4994	$200.50	$200.50	$200.50
Purchase #2	$85.89	4.715%	$89.9397	$89.94	$89.95	$89.90
Purchase #3	$74.82	9.270%	$81.7558	$81.76	$81.75	$81.80
Purchase #4	$36.59	8.477%	$39.6917	$39.69	$39.70	$39.70
Purchase #5	$175.69	5.177%	$184.7855	$184.79	$184.80	$184.80
Purchase #6	$232.25	9.299%	$253.8469	$253.85	$253.85	$253.80
Purchase #7	$65.55	8.836%	$71.342	$71.34	$71.35	$71.30
7 purchase totals =	$855.40		$921.8610	$921.87	$921.90	$921.80