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	$88.65	12.405%	$99.647	$99.65	$99.65	$99.60
Purchase #2	$194.85	9.208%	$212.7918	$212.79	$212.80	$212.80
Purchase #3	$64.47	12.257%	$72.3721	$72.37	$72.35	$72.40
Purchase #4	$206.34	9.176%	$225.2738	$225.27	$225.25	$225.30
Purchase #5	$41.92	11.765%	$46.8519	$46.85	$46.85	$46.90
Purchase #6	$161.52	8.665%	$175.5157	$175.52	$175.50	$175.50
Purchase #7	$20.52	9.407%	$22.4503	$22.45	$22.45	$22.50
7 purchase totals =	$778.27		$854.9026	$854.90	$854.85	$855.00