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	$73.67	13.405%	$83.5455	$83.55	$83.55	$83.50
Purchase #2	$194.30	8.556%	$210.9243	$210.92	$210.90	$210.90
Purchase #3	$210.82	11.739%	$235.5682	$235.57	$235.55	$235.60
Purchase #4	$241.83	9.118%	$263.8801	$263.88	$263.90	$263.90
Purchase #5	$181.81	10.187%	$200.331	$200.33	$200.35	$200.30
Purchase #6	$28.81	10.805%	$31.9229	$31.92	$31.90	$31.90
Purchase #7	$167.77	12.733%	$189.1322	$189.13	$189.15	$189.10
7 purchase totals =	$1,099.01		$1,215.3042	$1,215.30	$1,215.30	$1,215.20