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	$7.49	5.721%	$7.9185	$7.92	$7.90	$7.90
Purchase #2	$24.67	4.292%	$25.7288	$25.73	$25.75	$25.70
Purchase #3	$149.82	12.367%	$168.3482	$168.35	$168.35	$168.30
Purchase #4	$175.89	8.510%	$190.8582	$190.86	$190.85	$190.90
Purchase #5	$172.83	5.688%	$182.6606	$182.66	$182.65	$182.70
Purchase #6	$187.66	9.398%	$205.2963	$205.30	$205.30	$205.30
Purchase #7	$47.96	11.631%	$53.5382	$53.54	$53.55	$53.50
7 purchase totals =	$766.32		$834.3488	$834.36	$834.35	$834.30