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	$82.50	9.682%	$90.4877	$90.49	$90.50	$90.50
Purchase #2	$89.80	12.768%	$101.2657	$101.27	$101.25	$101.30
Purchase #3	$212.88	5.158%	$223.8604	$223.86	$223.85	$223.90
Purchase #4	$126.68	9.397%	$138.5841	$138.58	$138.60	$138.60
Purchase #5	$185.28	7.235%	$198.685	$198.69	$198.70	$198.70
Purchase #6	$71.72	10.867%	$79.5138	$79.51	$79.50	$79.50
Purchase #7	$155.91	7.268%	$167.2415	$167.24	$167.25	$167.20
7 purchase totals =	$924.77		$999.6382	$999.64	$999.65	$999.70