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	$39.72	6.489%	$42.2974	$42.30	$42.30	$42.30
Purchase #2	$111.75	6.295%	$118.7847	$118.78	$118.80	$118.80
Purchase #3	$17.30	5.638%	$18.2754	$18.28	$18.30	$18.30
Purchase #4	$80.39	3.631%	$83.309	$83.31	$83.30	$83.30
Purchase #5	$229.63	4.750%	$240.5374	$240.54	$240.55	$240.50
Purchase #6	$55.59	3.545%	$57.5607	$57.56	$57.55	$57.60
Purchase #7	$196.92	6.543%	$209.8045	$209.80	$209.80	$209.80
7 purchase totals =	$731.30		$770.5691	$770.57	$770.60	$770.60