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	$54.86	10.300%	$60.5106	$60.51	$60.50	$60.50
Purchase #2	$23.97	13.319%	$27.1626	$27.16	$27.15	$27.20
Purchase #3	$195.35	13.851%	$222.4079	$222.41	$222.40	$222.40
Purchase #4	$203.61	8.549%	$221.0166	$221.02	$221.00	$221.00
Purchase #5	$240.80	10.189%	$265.3351	$265.34	$265.35	$265.30
Purchase #6	$127.65	3.320%	$131.888	$131.89	$131.90	$131.90
Purchase #7	$60.59	8.376%	$65.665	$65.67	$65.65	$65.70
7 purchase totals =	$906.83		$993.9858	$994.00	$993.95	$994.00