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	$152.62	13.818%	$173.709	$173.71	$173.70	$173.70
Purchase #2	$178.50	10.204%	$196.7141	$196.71	$196.70	$196.70
Purchase #3	$133.25	4.107%	$138.7226	$138.72	$138.70	$138.70
Purchase #4	$59.73	3.500%	$61.8206	$61.82	$61.80	$61.80
Purchase #5	$247.52	8.155%	$267.7053	$267.71	$267.70	$267.70
Purchase #6	$50.89	13.640%	$57.8314	$57.83	$57.85	$57.80
Purchase #7	$101.43	13.438%	$115.0602	$115.06	$115.05	$115.10
7 purchase totals =	$923.94		$1,011.5632	$1,011.56	$1,011.50	$1,011.50