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	$121.85	7.481%	$130.9656	$130.97	$130.95	$131.00
Purchase #2	$94.29	6.122%	$100.0624	$100.06	$100.05	$100.10
Purchase #3	$117.78	11.762%	$131.6333	$131.63	$131.65	$131.60
Purchase #4	$73.57	10.211%	$81.0822	$81.08	$81.10	$81.10
Purchase #5	$65.86	10.184%	$72.5672	$72.57	$72.55	$72.60
Purchase #6	$147.43	13.148%	$166.8141	$166.81	$166.80	$166.80
Purchase #7	$188.94	10.709%	$209.1736	$209.17	$209.15	$209.20
7 purchase totals =	$809.72		$892.2984	$892.29	$892.25	$892.40