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	$109.61	12.674%	$123.502	$123.50	$123.50	$123.50
Purchase #2	$128.42	7.248%	$137.7279	$137.73	$137.75	$137.70
Purchase #3	$103.47	9.590%	$113.3928	$113.39	$113.40	$113.40
Purchase #4	$96.36	6.187%	$102.3218	$102.32	$102.30	$102.30
Purchase #5	$107.33	8.411%	$116.3575	$116.36	$116.35	$116.40
Purchase #6	$82.65	10.779%	$91.5588	$91.56	$91.55	$91.60
Purchase #7	$111.34	11.173%	$123.78	$123.78	$123.80	$123.80
7 purchase totals =	$739.18		$808.6408	$808.64	$808.65	$808.70