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	$213.65	13.321%	$242.1103	$242.11	$242.10	$242.10
Purchase #2	$70.90	10.416%	$78.2849	$78.28	$78.30	$78.30
Purchase #3	$171.61	11.660%	$191.6197	$191.62	$191.60	$191.60
Purchase #4	$16.46	7.121%	$17.6321	$17.63	$17.65	$17.60
Purchase #5	$106.38	3.708%	$110.3246	$110.32	$110.30	$110.30
Purchase #6	$74.36	5.788%	$78.664	$78.66	$78.65	$78.70
Purchase #7	$37.62	4.381%	$39.2681	$39.27	$39.25	$39.30
7 purchase totals =	$690.98		$757.9037	$757.89	$757.85	$757.90