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	$35.52	3.306%	$36.6943	$36.69	$36.70	$36.70
Purchase #2	$127.36	7.694%	$137.1591	$137.16	$137.15	$137.20
Purchase #3	$169.83	7.105%	$181.8964	$181.90	$181.90	$181.90
Purchase #4	$38.97	4.735%	$40.8152	$40.82	$40.80	$40.80
Purchase #5	$43.56	9.233%	$47.5819	$47.58	$47.60	$47.60
Purchase #6	$96.34	13.723%	$109.5607	$109.56	$109.55	$109.60
Purchase #7	$89.75	11.751%	$100.2965	$100.30	$100.30	$100.30
7 purchase totals =	$601.33		$654.0041	$654.01	$654.00	$654.10