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	$90.52	10.172%	$99.7277	$99.73	$99.75	$99.70
Purchase #2	$18.93	11.530%	$21.1126	$21.11	$21.10	$21.10
Purchase #3	$196.32	11.704%	$219.2973	$219.30	$219.30	$219.30
Purchase #4	$225.52	9.359%	$246.6264	$246.63	$246.65	$246.60
Purchase #5	$182.56	3.288%	$188.5626	$188.56	$188.55	$188.60
Purchase #6	$75.88	7.645%	$81.681	$81.68	$81.70	$81.70
Purchase #7	$215.32	4.308%	$224.596	$224.60	$224.60	$224.60
7 purchase totals =	$1,005.05		$1,081.6036	$1,081.61	$1,081.65	$1,081.60