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	$13.55	12.653%	$15.2645	$15.26	$15.25	$15.30
Purchase #2	$102.37	9.800%	$112.4023	$112.40	$112.40	$112.40
Purchase #3	$33.79	6.254%	$35.9032	$35.90	$35.90	$35.90
Purchase #4	$166.32	13.318%	$188.4705	$188.47	$188.45	$188.50
Purchase #5	$45.36	4.738%	$47.5092	$47.51	$47.50	$47.50
Purchase #6	$135.61	11.233%	$150.8431	$150.84	$150.85	$150.80
Purchase #7	$35.37	7.219%	$37.9234	$37.92	$37.90	$37.90
7 purchase totals =	$532.37		$588.3162	$588.30	$588.25	$588.30