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	$227.53	13.499%	$258.2443	$258.24	$258.25	$258.20
Purchase #2	$56.84	8.837%	$61.863	$61.86	$61.85	$61.90
Purchase #3	$176.27	8.179%	$190.6871	$190.69	$190.70	$190.70
Purchase #4	$228.68	6.607%	$243.7889	$243.79	$243.80	$243.80
Purchase #5	$118.70	9.863%	$130.4074	$130.41	$130.40	$130.40
Purchase #6	$6.96	11.828%	$7.7832	$7.78	$7.80	$7.80
Purchase #7	$131.86	4.418%	$137.6856	$137.69	$137.70	$137.70
7 purchase totals =	$946.84		$1,030.4595	$1,030.46	$1,030.50	$1,030.50