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	$118.85	4.523%	$124.2256	$124.23	$124.25	$124.20
Purchase #2	$178.42	13.500%	$202.5067	$202.51	$202.50	$202.50
Purchase #3	$89.31	11.772%	$99.8236	$99.82	$99.80	$99.80
Purchase #4	$39.66	6.355%	$42.1804	$42.18	$42.20	$42.20
Purchase #5	$48.36	9.667%	$53.035	$53.04	$53.05	$53.00
Purchase #6	$85.91	10.559%	$94.9812	$94.98	$95.00	$95.00
Purchase #7	$65.56	6.132%	$69.5801	$69.58	$69.60	$69.60
7 purchase totals =	$626.07		$686.3326	$686.34	$686.40	$686.30