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	$160.34	12.115%	$179.7652	$179.77	$179.75	$179.80
Purchase #2	$168.43	13.235%	$190.7217	$190.72	$190.70	$190.70
Purchase #3	$192.77	6.386%	$205.0803	$205.08	$205.10	$205.10
Purchase #4	$160.66	11.340%	$178.8788	$178.88	$178.90	$178.90
Purchase #5	$230.33	6.535%	$245.3821	$245.38	$245.40	$245.40
Purchase #6	$51.30	5.531%	$54.1374	$54.14	$54.15	$54.10
Purchase #7	$185.98	7.713%	$200.3246	$200.32	$200.30	$200.30
7 purchase totals =	$1,149.81		$1,254.2901	$1,254.29	$1,254.30	$1,254.30