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	$38.48	9.578%	$42.1656	$42.17	$42.15	$42.20
Purchase #2	$130.86	5.303%	$137.7995	$137.80	$137.80	$137.80
Purchase #3	$157.49	6.831%	$168.2481	$168.25	$168.25	$168.20
Purchase #4	$36.90	3.590%	$38.2247	$38.22	$38.20	$38.20
Purchase #5	$139.28	6.498%	$148.3304	$148.33	$148.35	$148.30
Purchase #6	$186.45	4.717%	$195.2448	$195.24	$195.25	$195.20
Purchase #7	$50.93	10.864%	$56.463	$56.46	$56.45	$56.50
7 purchase totals =	$740.39		$786.4761	$786.47	$786.45	$786.40