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	$50.55	9.258%	$55.2299	$55.23	$55.25	$55.20
Purchase #2	$145.73	3.356%	$150.6207	$150.62	$150.60	$150.60
Purchase #3	$116.88	4.693%	$122.3652	$122.37	$122.35	$122.40
Purchase #4	$240.27	12.751%	$270.9068	$270.91	$270.90	$270.90
Purchase #5	$154.42	3.764%	$160.2324	$160.23	$160.25	$160.20
Purchase #6	$225.47	13.740%	$256.4496	$256.45	$256.45	$256.40
Purchase #7	$32.51	3.637%	$33.6924	$33.69	$33.70	$33.70
7 purchase totals =	$965.83		$1,049.4970	$1,049.50	$1,049.50	$1,049.40