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	$249.99	13.672%	$284.1686	$284.17	$284.15	$284.20
Purchase #2	$37.52	11.535%	$41.8479	$41.85	$41.85	$41.80
Purchase #3	$129.25	9.499%	$141.5275	$141.53	$141.55	$141.50
Purchase #4	$111.54	12.461%	$125.439	$125.44	$125.45	$125.40
Purchase #5	$76.61	11.453%	$85.3841	$85.38	$85.40	$85.40
Purchase #6	$186.78	7.409%	$200.6185	$200.62	$200.60	$200.60
Purchase #7	$130.96	13.388%	$148.4929	$148.49	$148.50	$148.50
7 purchase totals =	$922.65		$1,027.4785	$1,027.48	$1,027.50	$1,027.40