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	$84.88	6.796%	$90.6484	$90.65	$90.65	$90.60
Purchase #2	$192.35	9.483%	$210.5906	$210.59	$210.60	$210.60
Purchase #3	$122.60	13.756%	$139.4649	$139.46	$139.45	$139.50
Purchase #4	$142.26	7.452%	$152.8612	$152.86	$152.85	$152.90
Purchase #5	$13.84	9.503%	$15.1552	$15.16	$15.15	$15.20
Purchase #6	$249.81	7.106%	$267.5615	$267.56	$267.55	$267.60
Purchase #7	$150.26	3.865%	$156.0675	$156.07	$156.05	$156.10
7 purchase totals =	$956.00		$1,032.3493	$1,032.35	$1,032.30	$1,032.50