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	$121.35	13.528%	$137.7662	$137.77	$137.75	$137.80
Purchase #2	$185.74	5.596%	$196.134	$196.13	$196.15	$196.10
Purchase #3	$216.29	10.177%	$238.3018	$238.30	$238.30	$238.30
Purchase #4	$80.30	11.624%	$89.6341	$89.63	$89.65	$89.60
Purchase #5	$31.77	10.173%	$35.002	$35.00	$35.00	$35.00
Purchase #6	$147.46	13.364%	$167.1666	$167.17	$167.15	$167.20
Purchase #7	$230.53	7.769%	$248.4399	$248.44	$248.45	$248.40
7 purchase totals =	$1,013.44		$1,112.4446	$1,112.44	$1,112.45	$1,112.40