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	$86.40	3.265%	$89.221	$89.22	$89.20	$89.20
Purchase #2	$221.84	12.859%	$250.3664	$250.37	$250.35	$250.40
Purchase #3	$69.35	6.871%	$74.115	$74.12	$74.10	$74.10
Purchase #4	$52.55	4.295%	$54.807	$54.81	$54.80	$54.80
Purchase #5	$223.67	7.248%	$239.8816	$239.88	$239.90	$239.90
Purchase #6	$136.99	10.399%	$151.2356	$151.24	$151.25	$151.20
Purchase #7	$139.63	11.682%	$155.9416	$155.94	$155.95	$155.90
7 purchase totals =	$930.43		$1,015.5682	$1,015.58	$1,015.55	$1,015.50