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	$45.69	10.546%	$50.5085	$50.51	$50.50	$50.50
Purchase #2	$24.68	3.538%	$25.5532	$25.55	$25.55	$25.60
Purchase #3	$133.89	12.707%	$150.9034	$150.90	$150.90	$150.90
Purchase #4	$168.87	13.613%	$191.8583	$191.86	$191.85	$191.90
Purchase #5	$218.25	4.486%	$228.0407	$228.04	$228.05	$228.00
Purchase #6	$159.55	7.478%	$171.4811	$171.48	$171.50	$171.50
Purchase #7	$123.99	12.623%	$139.6413	$139.64	$139.65	$139.60
7 purchase totals =	$874.92		$957.9865	$957.98	$958.00	$958.00