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	$65.74	10.240%	$72.4718	$72.47	$72.45	$72.50
Purchase #2	$96.86	4.512%	$101.2303	$101.23	$101.25	$101.20
Purchase #3	$77.37	4.459%	$80.8199	$80.82	$80.80	$80.80
Purchase #4	$89.74	11.252%	$99.8375	$99.84	$99.85	$99.80
Purchase #5	$51.78	12.490%	$58.2473	$58.25	$58.25	$58.20
Purchase #6	$77.62	9.799%	$85.226	$85.23	$85.25	$85.20
Purchase #7	$69.29	4.565%	$72.4531	$72.45	$72.45	$72.50
7 purchase totals =	$528.40		$570.2859	$570.29	$570.30	$570.20