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	$72.78	7.178%	$78.0041	$78.00	$78.00	$78.00
Purchase #2	$118.41	8.441%	$128.405	$128.41	$128.40	$128.40
Purchase #3	$236.44	6.301%	$251.3381	$251.34	$251.35	$251.30
Purchase #4	$98.26	11.288%	$109.3516	$109.35	$109.35	$109.40
Purchase #5	$196.81	11.804%	$220.0415	$220.04	$220.05	$220.00
Purchase #6	$123.99	11.134%	$137.795	$137.80	$137.80	$137.80
Purchase #7	$161.39	10.529%	$178.3828	$178.38	$178.40	$178.40
7 purchase totals =	$1,008.08		$1,103.3181	$1,103.32	$1,103.35	$1,103.30