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	$163.33	13.780%	$185.8369	$185.84	$185.85	$185.80
Purchase #2	$213.92	9.531%	$234.3087	$234.31	$234.30	$234.30
Purchase #3	$74.47	12.450%	$83.7415	$83.74	$83.75	$83.70
Purchase #4	$31.45	11.827%	$35.1696	$35.17	$35.15	$35.20
Purchase #5	$142.53	9.124%	$155.5344	$155.53	$155.55	$155.50
Purchase #6	$225.91	12.828%	$254.8897	$254.89	$254.90	$254.90
Purchase #7	$33.89	13.540%	$38.4787	$38.48	$38.50	$38.50
7 purchase totals =	$885.50		$987.9595	$987.96	$988.00	$987.90