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	$250.96	11.377%	$279.5117	$279.51	$279.50	$279.50
Purchase #2	$245.45	12.248%	$275.5127	$275.51	$275.50	$275.50
Purchase #3	$180.35	6.170%	$191.4776	$191.48	$191.50	$191.50
Purchase #4	$13.43	3.218%	$13.8622	$13.86	$13.85	$13.90
Purchase #5	$221.63	12.272%	$248.8284	$248.83	$248.85	$248.80
Purchase #6	$178.85	5.383%	$188.4775	$188.48	$188.50	$188.50
Purchase #7	$39.51	5.702%	$41.7629	$41.76	$41.75	$41.80
7 purchase totals =	$1,130.18		$1,239.4330	$1,239.43	$1,239.45	$1,239.50