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	$135.61	6.234%	$144.0639	$144.06	$144.05	$144.10
Purchase #2	$93.52	4.220%	$97.4665	$97.47	$97.45	$97.50
Purchase #3	$28.97	7.232%	$31.0651	$31.07	$31.05	$31.10
Purchase #4	$65.78	9.801%	$72.2271	$72.23	$72.25	$72.20
Purchase #5	$37.90	11.253%	$42.1649	$42.16	$42.15	$42.20
Purchase #6	$102.27	13.603%	$116.1818	$116.18	$116.20	$116.20
Purchase #7	$107.44	9.653%	$117.8112	$117.81	$117.80	$117.80
7 purchase totals =	$571.49		$620.9805	$620.98	$620.95	$621.10