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	$63.29	11.854%	$70.7924	$70.79	$70.80	$70.80
Purchase #2	$175.91	5.242%	$185.1312	$185.13	$185.15	$185.10
Purchase #3	$70.71	10.364%	$78.0384	$78.04	$78.05	$78.00
Purchase #4	$110.91	5.277%	$116.7627	$116.76	$116.75	$116.80
Purchase #5	$58.35	6.346%	$62.0529	$62.05	$62.05	$62.10
Purchase #6	$156.82	4.801%	$164.3489	$164.35	$164.35	$164.30
Purchase #7	$42.33	3.774%	$43.9275	$43.93	$43.95	$43.90
7 purchase totals =	$678.32		$721.0540	$721.05	$721.10	$721.00