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	$9.56	7.469%	$10.274	$10.27	$10.25	$10.30
Purchase #2	$24.67	4.621%	$25.81	$25.81	$25.80	$25.80
Purchase #3	$69.70	12.369%	$78.3212	$78.32	$78.30	$78.30
Purchase #4	$74.51	5.138%	$78.3383	$78.34	$78.35	$78.30
Purchase #5	$196.76	5.365%	$207.3162	$207.32	$207.30	$207.30
Purchase #6	$194.76	8.824%	$211.9456	$211.95	$211.95	$211.90
Purchase #7	$29.77	12.421%	$33.4677	$33.47	$33.45	$33.50
7 purchase totals =	$599.73		$645.4730	$645.48	$645.40	$645.40