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	$115.83	13.342%	$131.284	$131.28	$131.30	$131.30
Purchase #2	$211.81	12.521%	$238.3307	$238.33	$238.35	$238.30
Purchase #3	$89.96	5.561%	$94.9627	$94.96	$94.95	$95.00
Purchase #4	$210.70	11.792%	$235.5457	$235.55	$235.55	$235.50
Purchase #5	$204.65	3.661%	$212.1422	$212.14	$212.15	$212.10
Purchase #6	$134.34	5.206%	$141.3337	$141.33	$141.35	$141.30
Purchase #7	$75.49	9.784%	$82.8759	$82.88	$82.90	$82.90
7 purchase totals =	$1,042.78		$1,136.4749	$1,136.47	$1,136.55	$1,136.40