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	$32.51	12.258%	$36.4951	$36.50	$36.50	$36.50
Purchase #2	$59.37	7.842%	$64.0258	$64.03	$64.05	$64.00
Purchase #3	$76.73	11.159%	$85.2923	$85.29	$85.30	$85.30
Purchase #4	$54.47	13.661%	$61.9111	$61.91	$61.90	$61.90
Purchase #5	$211.97	5.535%	$223.7025	$223.70	$223.70	$223.70
Purchase #6	$17.76	7.338%	$19.0632	$19.06	$19.05	$19.10
Purchase #7	$5.83	10.168%	$6.4228	$6.42	$6.40	$6.40
7 purchase totals =	$458.64		$496.9128	$496.91	$496.90	$496.90