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	$166.85	12.170%	$187.1556	$187.16	$187.15	$187.20
Purchase #2	$101.62	10.157%	$111.9415	$111.94	$111.95	$111.90
Purchase #3	$89.57	3.298%	$92.524	$92.52	$92.50	$92.50
Purchase #4	$64.62	3.206%	$66.6917	$66.69	$66.70	$66.70
Purchase #5	$92.85	11.285%	$103.3281	$103.33	$103.35	$103.30
Purchase #6	$129.54	9.367%	$141.674	$141.67	$141.65	$141.70
Purchase #7	$91.28	5.179%	$96.0074	$96.01	$96.00	$96.00
7 purchase totals =	$736.33		$799.3223	$799.32	$799.30	$799.30