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	$245.79	13.236%	$278.3228	$278.32	$278.30	$278.30
Purchase #2	$192.83	9.202%	$210.5742	$210.57	$210.55	$210.60
Purchase #3	$182.71	4.850%	$191.5714	$191.57	$191.55	$191.60
Purchase #4	$207.59	7.207%	$222.551	$222.55	$222.55	$222.60
Purchase #5	$184.90	8.606%	$200.8125	$200.81	$200.80	$200.80
Purchase #6	$5.93	7.204%	$6.3572	$6.36	$6.35	$6.40
Purchase #7	$54.96	11.648%	$61.3617	$61.36	$61.35	$61.40
7 purchase totals =	$1,074.71		$1,171.5508	$1,171.54	$1,171.45	$1,171.70