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	$215.92	3.239%	$222.9136	$222.91	$222.90	$222.90
Purchase #2	$75.31	8.164%	$81.4583	$81.46	$81.45	$81.50
Purchase #3	$40.54	4.243%	$42.2601	$42.26	$42.25	$42.30
Purchase #4	$16.80	11.533%	$18.7375	$18.74	$18.75	$18.70
Purchase #5	$233.42	12.529%	$262.6652	$262.67	$262.65	$262.70
Purchase #6	$105.45	4.130%	$109.8051	$109.81	$109.80	$109.80
Purchase #7	$105.52	6.480%	$112.3577	$112.36	$112.35	$112.40
7 purchase totals =	$792.96		$850.1975	$850.21	$850.15	$850.30