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	$15.31	5.148%	$16.0982	$16.10	$16.10	$16.10
Purchase #2	$128.34	11.228%	$142.75	$142.75	$142.75	$142.80
Purchase #3	$18.91	7.354%	$20.3006	$20.30	$20.30	$20.30
Purchase #4	$89.50	13.221%	$101.3328	$101.33	$101.35	$101.30
Purchase #5	$95.89	8.281%	$103.8307	$103.83	$103.85	$103.80
Purchase #6	$151.80	5.128%	$159.5843	$159.58	$159.60	$159.60
Purchase #7	$212.92	12.157%	$238.8047	$238.80	$238.80	$238.80
7 purchase totals =	$712.67		$782.7013	$782.69	$782.75	$782.70