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	$232.67	4.247%	$242.5515	$242.55	$242.55	$242.60
Purchase #2	$116.96	12.778%	$131.9051	$131.91	$131.90	$131.90
Purchase #3	$83.52	6.791%	$89.1918	$89.19	$89.20	$89.20
Purchase #4	$199.67	9.333%	$218.3052	$218.31	$218.30	$218.30
Purchase #5	$121.55	13.305%	$137.7222	$137.72	$137.70	$137.70
Purchase #6	$147.32	5.429%	$155.318	$155.32	$155.30	$155.30
Purchase #7	$109.92	11.489%	$122.5487	$122.55	$122.55	$122.50
7 purchase totals =	$1,011.61		$1,097.5425	$1,097.55	$1,097.50	$1,097.50