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	$12.72	6.208%	$13.5097	$13.51	$13.50	$13.50
Purchase #2	$42.44	6.285%	$45.1074	$45.11	$45.10	$45.10
Purchase #3	$109.89	13.134%	$124.323	$124.32	$124.30	$124.30
Purchase #4	$219.59	3.868%	$228.0837	$228.08	$228.10	$228.10
Purchase #5	$41.97	11.556%	$46.8201	$46.82	$46.80	$46.80
Purchase #6	$139.55	4.249%	$145.4795	$145.48	$145.50	$145.50
Purchase #7	$230.39	10.654%	$254.9358	$254.94	$254.95	$254.90
7 purchase totals =	$796.55		$858.2592	$858.26	$858.25	$858.20