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	$33.42	6.848%	$35.7086	$35.71	$35.70	$35.70
Purchase #2	$131.59	6.150%	$139.6828	$139.68	$139.70	$139.70
Purchase #3	$47.95	9.828%	$52.6625	$52.66	$52.65	$52.70
Purchase #4	$7.83	5.329%	$8.2473	$8.25	$8.25	$8.20
Purchase #5	$128.31	10.629%	$141.9481	$141.95	$141.95	$141.90
Purchase #6	$108.33	13.802%	$123.2817	$123.28	$123.30	$123.30
Purchase #7	$12.97	7.106%	$13.8916	$13.89	$13.90	$13.90
7 purchase totals =	$470.40		$515.4226	$515.42	$515.45	$515.40