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	$178.61	6.111%	$189.5249	$189.52	$189.50	$189.50
Purchase #2	$169.47	8.783%	$184.3546	$184.35	$184.35	$184.40
Purchase #3	$19.83	10.207%	$21.854	$21.85	$21.85	$21.90
Purchase #4	$145.65	3.419%	$150.6298	$150.63	$150.65	$150.60
Purchase #5	$210.72	8.784%	$229.2296	$229.23	$229.25	$229.20
Purchase #6	$72.70	7.420%	$78.0943	$78.09	$78.10	$78.10
Purchase #7	$109.84	13.475%	$124.6409	$124.64	$124.65	$124.60
7 purchase totals =	$906.82		$978.3281	$978.31	$978.35	$978.30