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	$71.91	9.193%	$78.5207	$78.52	$78.50	$78.50
Purchase #2	$99.40	4.173%	$103.548	$103.55	$103.55	$103.50
Purchase #3	$242.93	11.550%	$270.9884	$270.99	$271.00	$271.00
Purchase #4	$75.46	6.581%	$80.426	$80.43	$80.45	$80.40
Purchase #5	$37.68	13.770%	$42.8685	$42.87	$42.85	$42.90
Purchase #6	$163.69	7.211%	$175.4937	$175.49	$175.50	$175.50
Purchase #7	$175.47	11.717%	$196.0298	$196.03	$196.05	$196.00
7 purchase totals =	$866.54		$947.8751	$947.88	$947.90	$947.80