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	$215.29	10.782%	$238.5026	$238.50	$238.50	$238.50
Purchase #2	$153.92	11.443%	$171.5331	$171.53	$171.55	$171.50
Purchase #3	$18.88	12.117%	$21.1677	$21.17	$21.15	$21.20
Purchase #4	$27.36	8.428%	$29.6659	$29.67	$29.65	$29.70
Purchase #5	$27.28	6.694%	$29.1061	$29.11	$29.10	$29.10
Purchase #6	$63.91	13.512%	$72.5455	$72.55	$72.55	$72.50
Purchase #7	$93.77	10.295%	$103.4236	$103.42	$103.40	$103.40
7 purchase totals =	$600.41		$665.9445	$665.95	$665.90	$665.90