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	$133.90	7.129%	$143.4457	$143.45	$143.45	$143.40
Purchase #2	$230.94	9.822%	$253.6229	$253.62	$253.60	$253.60
Purchase #3	$185.43	7.715%	$199.7359	$199.74	$199.75	$199.70
Purchase #4	$36.33	13.529%	$41.2451	$41.25	$41.25	$41.20
Purchase #5	$97.28	11.276%	$108.2493	$108.25	$108.25	$108.20
Purchase #6	$55.25	7.365%	$59.3192	$59.32	$59.30	$59.30
Purchase #7	$69.99	12.751%	$78.9144	$78.91	$78.90	$78.90
7 purchase totals =	$809.12		$884.5325	$884.54	$884.50	$884.30