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	$97.96	7.674%	$105.4775	$105.48	$105.50	$105.50
Purchase #2	$119.37	10.170%	$131.5099	$131.51	$131.50	$131.50
Purchase #3	$164.85	12.782%	$185.9211	$185.92	$185.90	$185.90
Purchase #4	$209.49	5.675%	$221.3786	$221.38	$221.40	$221.40
Purchase #5	$29.49	13.360%	$33.4299	$33.43	$33.45	$33.40
Purchase #6	$39.33	7.751%	$42.3785	$42.38	$42.40	$42.40
Purchase #7	$218.94	13.526%	$248.5538	$248.55	$248.55	$248.60
7 purchase totals =	$879.43		$968.6493	$968.65	$968.70	$968.70