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	$24.52	10.158%	$27.0107	$27.01	$27.00	$27.00
Purchase #2	$30.71	12.154%	$34.4425	$34.44	$34.45	$34.40
Purchase #3	$167.85	4.791%	$175.8917	$175.89	$175.90	$175.90
Purchase #4	$243.43	5.413%	$256.6069	$256.61	$256.60	$256.60
Purchase #5	$157.72	11.532%	$175.9083	$175.91	$175.90	$175.90
Purchase #6	$134.34	9.701%	$147.3723	$147.37	$147.35	$147.40
Purchase #7	$32.83	13.727%	$37.3366	$37.34	$37.35	$37.30
7 purchase totals =	$791.40		$854.5690	$854.57	$854.55	$854.50