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	$138.94	4.298%	$144.9116	$144.91	$144.90	$144.90
Purchase #2	$222.94	6.869%	$238.2537	$238.25	$238.25	$238.30
Purchase #3	$72.79	8.554%	$79.0165	$79.02	$79.00	$79.00
Purchase #4	$158.89	8.480%	$172.3639	$172.36	$172.35	$172.40
Purchase #5	$211.89	11.160%	$235.5369	$235.54	$235.55	$235.50
Purchase #6	$89.63	4.792%	$93.9251	$93.93	$93.95	$93.90
Purchase #7	$57.48	9.117%	$62.7205	$62.72	$62.70	$62.70
7 purchase totals =	$952.56		$1,026.7282	$1,026.73	$1,026.70	$1,026.70