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	$142.67	13.768%	$162.3128	$162.31	$162.30	$162.30
Purchase #2	$194.49	9.808%	$213.5656	$213.57	$213.55	$213.60
Purchase #3	$52.68	13.265%	$59.668	$59.67	$59.65	$59.70
Purchase #4	$186.26	9.463%	$203.8858	$203.89	$203.90	$203.90
Purchase #5	$160.90	7.696%	$173.2829	$173.28	$173.30	$173.30
Purchase #6	$19.63	6.526%	$20.9111	$20.91	$20.90	$20.90
Purchase #7	$64.41	3.224%	$66.4866	$66.49	$66.50	$66.50
7 purchase totals =	$821.04		$900.1128	$900.12	$900.10	$900.20