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	$154.51	7.360%	$165.8819	$165.88	$165.90	$165.90
Purchase #2	$46.28	3.490%	$47.8952	$47.90	$47.90	$47.90
Purchase #3	$17.36	9.502%	$19.0095	$19.01	$19.00	$19.00
Purchase #4	$76.33	3.197%	$78.7703	$78.77	$78.75	$78.80
Purchase #5	$30.97	8.340%	$33.5529	$33.55	$33.55	$33.60
Purchase #6	$34.29	4.777%	$35.928	$35.93	$35.95	$35.90
Purchase #7	$168.79	12.133%	$189.2693	$189.27	$189.25	$189.30
7 purchase totals =	$528.53		$570.3071	$570.31	$570.30	$570.40