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	$74.42	5.516%	$78.525	$78.53	$78.55	$78.50
Purchase #2	$177.45	6.360%	$188.7358	$188.74	$188.75	$188.70
Purchase #3	$36.40	11.361%	$40.5354	$40.54	$40.55	$40.50
Purchase #4	$145.43	7.252%	$155.9766	$155.98	$156.00	$156.00
Purchase #5	$79.63	12.354%	$89.4675	$89.47	$89.45	$89.50
Purchase #6	$148.83	8.176%	$160.9983	$161.00	$161.00	$161.00
Purchase #7	$225.34	3.539%	$233.3148	$233.31	$233.30	$233.30
7 purchase totals =	$887.50		$947.5534	$947.57	$947.60	$947.50