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	$92.58	8.818%	$100.7437	$100.74	$100.75	$100.70
Purchase #2	$184.69	11.491%	$205.9127	$205.91	$205.90	$205.90
Purchase #3	$55.43	6.678%	$59.1316	$59.13	$59.15	$59.10
Purchase #4	$72.95	3.349%	$75.3931	$75.39	$75.40	$75.40
Purchase #5	$113.88	5.651%	$120.3154	$120.32	$120.30	$120.30
Purchase #6	$215.81	7.376%	$231.7281	$231.73	$231.75	$231.70
Purchase #7	$44.90	3.809%	$46.6102	$46.61	$46.60	$46.60
7 purchase totals =	$780.24		$839.8348	$839.83	$839.85	$839.70