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	$80.71	10.600%	$89.2653	$89.27	$89.25	$89.30
Purchase #2	$146.84	9.176%	$160.314	$160.31	$160.30	$160.30
Purchase #3	$167.54	9.344%	$183.1949	$183.19	$183.20	$183.20
Purchase #4	$68.77	3.767%	$71.3606	$71.36	$71.35	$71.40
Purchase #5	$228.67	10.859%	$253.5013	$253.50	$253.50	$253.50
Purchase #6	$57.69	11.399%	$64.2661	$64.27	$64.25	$64.30
Purchase #7	$143.64	9.293%	$156.9885	$156.99	$157.00	$157.00
7 purchase totals =	$893.86		$978.8907	$978.89	$978.85	$979.00