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	$74.88	4.634%	$78.3499	$78.35	$78.35	$78.30
Purchase #2	$211.73	8.102%	$228.8844	$228.88	$228.90	$228.90
Purchase #3	$239.26	12.684%	$269.6077	$269.61	$269.60	$269.60
Purchase #4	$10.42	4.398%	$10.8783	$10.88	$10.90	$10.90
Purchase #5	$25.37	8.214%	$27.4539	$27.45	$27.45	$27.50
Purchase #6	$227.72	4.506%	$237.9811	$237.98	$238.00	$238.00
Purchase #7	$81.90	7.806%	$88.2931	$88.29	$88.30	$88.30
7 purchase totals =	$871.28		$941.4484	$941.44	$941.50	$941.50