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	$29.38	7.426%	$31.5618	$31.56	$31.55	$31.60
Purchase #2	$199.29	12.151%	$223.5057	$223.51	$223.50	$223.50
Purchase #3	$163.58	4.667%	$171.2143	$171.21	$171.20	$171.20
Purchase #4	$19.46	12.118%	$21.8182	$21.82	$21.80	$21.80
Purchase #5	$19.53	3.641%	$20.2411	$20.24	$20.25	$20.20
Purchase #6	$80.50	6.602%	$85.8146	$85.81	$85.80	$85.80
Purchase #7	$124.49	4.624%	$130.2464	$130.25	$130.25	$130.20
7 purchase totals =	$636.23		$684.4021	$684.40	$684.35	$684.30