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	$227.50	9.679%	$249.5197	$249.52	$249.50	$249.50
Purchase #2	$50.39	10.553%	$55.7077	$55.71	$55.70	$55.70
Purchase #3	$82.79	8.596%	$89.9066	$89.91	$89.90	$89.90
Purchase #4	$150.99	8.831%	$164.3239	$164.32	$164.30	$164.30
Purchase #5	$188.44	12.801%	$212.5622	$212.56	$212.55	$212.60
Purchase #6	$92.57	4.197%	$96.4552	$96.46	$96.45	$96.50
Purchase #7	$178.28	5.175%	$187.506	$187.51	$187.50	$187.50
7 purchase totals =	$970.96		$1,055.9813	$1,055.99	$1,055.90	$1,056.00