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	$90.68	10.229%	$99.9557	$99.96	$99.95	$100.00
Purchase #2	$69.42	5.601%	$73.3082	$73.31	$73.30	$73.30
Purchase #3	$62.40	8.824%	$67.9062	$67.91	$67.90	$67.90
Purchase #4	$127.73	13.401%	$144.8471	$144.85	$144.85	$144.80
Purchase #5	$182.69	6.665%	$194.8663	$194.87	$194.85	$194.90
Purchase #6	$61.46	9.474%	$67.2827	$67.28	$67.30	$67.30
Purchase #7	$170.83	7.701%	$183.9856	$183.99	$184.00	$184.00
7 purchase totals =	$765.21		$832.1518	$832.17	$832.15	$832.20