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	$164.93	3.652%	$170.9532	$170.95	$170.95	$171.00
Purchase #2	$195.82	12.240%	$219.7884	$219.79	$219.80	$219.80
Purchase #3	$167.31	13.321%	$189.5974	$189.60	$189.60	$189.60
Purchase #4	$46.54	4.452%	$48.612	$48.61	$48.60	$48.60
Purchase #5	$67.80	5.237%	$71.3507	$71.35	$71.35	$71.40
Purchase #6	$96.39	13.168%	$109.0826	$109.08	$109.10	$109.10
Purchase #7	$53.81	13.785%	$61.2277	$61.23	$61.25	$61.20
7 purchase totals =	$792.60		$870.6120	$870.61	$870.65	$870.70