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	$166.66	3.155%	$171.9181	$171.92	$171.90	$171.90
Purchase #2	$187.73	11.379%	$209.0918	$209.09	$209.10	$209.10
Purchase #3	$185.53	10.739%	$205.4541	$205.45	$205.45	$205.50
Purchase #4	$79.96	12.286%	$89.7839	$89.78	$89.80	$89.80
Purchase #5	$191.69	12.567%	$215.7797	$215.78	$215.80	$215.80
Purchase #6	$60.46	13.339%	$68.5248	$68.52	$68.50	$68.50
Purchase #7	$73.46	11.341%	$81.7911	$81.79	$81.80	$81.80
7 purchase totals =	$945.49		$1,042.3435	$1,042.33	$1,042.35	$1,042.40