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	$244.34	13.260%	$276.7395	$276.74	$276.75	$276.70
Purchase #2	$133.73	5.308%	$140.8284	$140.83	$140.85	$140.80
Purchase #3	$174.59	10.360%	$192.6775	$192.68	$192.70	$192.70
Purchase #4	$136.39	11.671%	$152.3081	$152.31	$152.30	$152.30
Purchase #5	$59.25	9.850%	$65.0861	$65.09	$65.10	$65.10
Purchase #6	$94.93	5.786%	$100.4226	$100.42	$100.40	$100.40
Purchase #7	$87.65	4.614%	$91.6942	$91.69	$91.70	$91.70
7 purchase totals =	$930.88		$1,019.7564	$1,019.76	$1,019.80	$1,019.70