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	$127.77	10.476%	$141.1552	$141.16	$141.15	$141.20
Purchase #2	$77.70	5.769%	$82.1825	$82.18	$82.20	$82.20
Purchase #3	$221.57	7.609%	$238.4293	$238.43	$238.45	$238.40
Purchase #4	$37.31	9.512%	$40.8589	$40.86	$40.85	$40.90
Purchase #5	$152.48	12.633%	$171.7428	$171.74	$171.75	$171.70
Purchase #6	$59.44	9.704%	$65.2081	$65.21	$65.20	$65.20
Purchase #7	$51.98	10.788%	$57.5876	$57.59	$57.60	$57.60
7 purchase totals =	$728.25		$797.1644	$797.17	$797.20	$797.20