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	$137.63	7.422%	$147.8449	$147.84	$147.85	$147.80
Purchase #2	$46.83	11.684%	$52.3016	$52.30	$52.30	$52.30
Purchase #3	$100.84	4.421%	$105.2981	$105.30	$105.30	$105.30
Purchase #4	$42.72	8.375%	$46.2978	$46.30	$46.30	$46.30
Purchase #5	$160.29	9.708%	$175.851	$175.85	$175.85	$175.90
Purchase #6	$39.26	6.558%	$41.8347	$41.83	$41.85	$41.80
Purchase #7	$106.98	11.735%	$119.5341	$119.53	$119.55	$119.50
7 purchase totals =	$634.55		$688.9622	$688.95	$689.00	$688.90