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	$14.56	12.227%	$16.3403	$16.34	$16.35	$16.30
Purchase #2	$119.51	4.498%	$124.8856	$124.89	$124.90	$124.90
Purchase #3	$81.35	10.219%	$89.6632	$89.66	$89.65	$89.70
Purchase #4	$180.49	3.564%	$186.9227	$186.92	$186.90	$186.90
Purchase #5	$48.60	4.459%	$50.7671	$50.77	$50.75	$50.80
Purchase #6	$12.44	11.854%	$13.9146	$13.91	$13.90	$13.90
Purchase #7	$40.57	12.709%	$45.726	$45.73	$45.75	$45.70
7 purchase totals =	$497.52		$528.2195	$528.22	$528.20	$528.20