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	$13.59	9.345%	$14.86	$14.86	$14.85	$14.90
Purchase #2	$170.52	8.441%	$184.9136	$184.91	$184.90	$184.90
Purchase #3	$66.63	6.686%	$71.0849	$71.08	$71.10	$71.10
Purchase #4	$46.38	6.739%	$49.5055	$49.51	$49.50	$49.50
Purchase #5	$125.40	13.365%	$142.1597	$142.16	$142.15	$142.20
Purchase #6	$31.59	13.519%	$35.8607	$35.86	$35.85	$35.90
Purchase #7	$232.89	13.708%	$264.8146	$264.81	$264.80	$264.80
7 purchase totals =	$687.00		$763.1990	$763.19	$763.15	$763.30