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	$123.54	12.185%	$138.5933	$138.59	$138.60	$138.60
Purchase #2	$80.84	12.587%	$91.0153	$91.02	$91.00	$91.00
Purchase #3	$156.41	11.695%	$174.7021	$174.70	$174.70	$174.70
Purchase #4	$72.90	7.261%	$78.1933	$78.19	$78.20	$78.20
Purchase #5	$170.35	6.514%	$181.4466	$181.45	$181.45	$181.40
Purchase #6	$123.54	12.552%	$139.0467	$139.05	$139.05	$139.00
Purchase #7	$125.90	10.646%	$139.3033	$139.30	$139.30	$139.30
7 purchase totals =	$853.48		$942.3006	$942.30	$942.30	$942.20