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	$29.85	4.142%	$31.0864	$31.09	$31.10	$31.10
Purchase #2	$176.31	7.298%	$189.1771	$189.18	$189.20	$189.20
Purchase #3	$229.72	9.175%	$250.7968	$250.80	$250.80	$250.80
Purchase #4	$25.92	9.306%	$28.3321	$28.33	$28.35	$28.30
Purchase #5	$65.78	7.111%	$70.4576	$70.46	$70.45	$70.50
Purchase #6	$76.54	12.665%	$86.2338	$86.23	$86.25	$86.20
Purchase #7	$37.31	7.535%	$40.1213	$40.12	$40.10	$40.10
7 purchase totals =	$641.43		$696.2051	$696.21	$696.25	$696.20