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	$232.59	9.396%	$254.4442	$254.44	$254.45	$254.40
Purchase #2	$35.38	6.724%	$37.759	$37.76	$37.75	$37.80
Purchase #3	$227.47	13.794%	$258.8472	$258.85	$258.85	$258.80
Purchase #4	$81.45	4.467%	$85.0884	$85.09	$85.10	$85.10
Purchase #5	$88.49	7.734%	$95.3338	$95.33	$95.35	$95.30
Purchase #6	$67.67	11.632%	$75.5414	$75.54	$75.55	$75.50
Purchase #7	$155.75	10.723%	$172.4511	$172.45	$172.45	$172.50
7 purchase totals =	$888.80		$979.4651	$979.46	$979.50	$979.40