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	$93.96	7.133%	$100.6622	$100.66	$100.65	$100.70
Purchase #2	$45.85	8.566%	$49.7775	$49.78	$49.80	$49.80
Purchase #3	$204.65	11.526%	$228.238	$228.24	$228.25	$228.20
Purchase #4	$160.49	12.287%	$180.2094	$180.21	$180.20	$180.20
Purchase #5	$89.65	9.597%	$98.2537	$98.25	$98.25	$98.30
Purchase #6	$134.49	12.691%	$151.5581	$151.56	$151.55	$151.60
Purchase #7	$189.86	10.403%	$209.6111	$209.61	$209.60	$209.60
7 purchase totals =	$918.95		$1,018.3100	$1,018.31	$1,018.30	$1,018.40