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	$55.33	3.592%	$57.3175	$57.32	$57.30	$57.30
Purchase #2	$198.52	10.607%	$219.577	$219.58	$219.60	$219.60
Purchase #3	$125.33	6.808%	$133.8625	$133.86	$133.85	$133.90
Purchase #4	$209.59	4.198%	$218.3886	$218.39	$218.40	$218.40
Purchase #5	$136.73	10.305%	$150.82	$150.82	$150.80	$150.80
Purchase #6	$61.65	5.847%	$65.2547	$65.25	$65.25	$65.30
Purchase #7	$58.51	10.515%	$64.6623	$64.66	$64.65	$64.70
7 purchase totals =	$845.66		$909.8826	$909.88	$909.85	$910.00