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	$223.49	11.801%	$249.8641	$249.86	$249.85	$249.90
Purchase #2	$84.40	6.530%	$89.9113	$89.91	$89.90	$89.90
Purchase #3	$101.38	7.252%	$108.7321	$108.73	$108.75	$108.70
Purchase #4	$184.41	7.453%	$198.1541	$198.15	$198.15	$198.20
Purchase #5	$31.51	4.346%	$32.8794	$32.88	$32.90	$32.90
Purchase #6	$95.69	3.256%	$98.8057	$98.81	$98.80	$98.80
Purchase #7	$180.47	4.710%	$188.9701	$188.97	$188.95	$189.00
7 purchase totals =	$901.35		$967.3168	$967.31	$967.30	$967.40