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	$30.27	9.356%	$33.1021	$33.10	$33.10	$33.10
Purchase #2	$85.48	6.350%	$90.908	$90.91	$90.90	$90.90
Purchase #3	$36.71	10.438%	$40.5418	$40.54	$40.55	$40.50
Purchase #4	$187.25	8.466%	$203.1026	$203.10	$203.10	$203.10
Purchase #5	$59.44	10.416%	$65.6313	$65.63	$65.65	$65.60
Purchase #6	$149.45	11.311%	$166.3543	$166.35	$166.35	$166.40
Purchase #7	$65.51	10.465%	$72.3656	$72.37	$72.35	$72.40
7 purchase totals =	$614.11		$672.0057	$672.00	$672.00	$672.00