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	$38.83	8.228%	$42.0249	$42.02	$42.00	$42.00
Purchase #2	$244.52	4.251%	$254.9145	$254.91	$254.90	$254.90
Purchase #3	$34.89	6.854%	$37.2814	$37.28	$37.30	$37.30
Purchase #4	$54.93	7.679%	$59.1481	$59.15	$59.15	$59.10
Purchase #5	$44.49	5.681%	$47.0175	$47.02	$47.00	$47.00
Purchase #6	$86.49	13.515%	$98.1791	$98.18	$98.20	$98.20
Purchase #7	$173.68	9.802%	$190.7041	$190.70	$190.70	$190.70
7 purchase totals =	$677.83		$729.2696	$729.26	$729.25	$729.20