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	$40.54	10.784%	$44.9118	$44.91	$44.90	$44.90
Purchase #2	$178.71	5.808%	$189.0895	$189.09	$189.10	$189.10
Purchase #3	$78.28	4.664%	$81.931	$81.93	$81.95	$81.90
Purchase #4	$59.33	8.415%	$64.3226	$64.32	$64.30	$64.30
Purchase #5	$48.68	5.497%	$51.3559	$51.36	$51.35	$51.40
Purchase #6	$178.34	6.244%	$189.4755	$189.48	$189.50	$189.50
Purchase #7	$109.76	12.425%	$123.3977	$123.40	$123.40	$123.40
7 purchase totals =	$693.64		$744.4840	$744.49	$744.50	$744.50