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	$6.55	3.355%	$6.7698	$6.77	$6.75	$6.80
Purchase #2	$249.37	4.809%	$261.3622	$261.36	$261.35	$261.40
Purchase #3	$75.29	13.641%	$85.5603	$85.56	$85.55	$85.60
Purchase #4	$13.26	10.344%	$14.6316	$14.63	$14.65	$14.60
Purchase #5	$136.85	7.132%	$146.6101	$146.61	$146.60	$146.60
Purchase #6	$78.54	13.743%	$89.3338	$89.33	$89.35	$89.30
Purchase #7	$129.83	10.464%	$143.4154	$143.42	$143.40	$143.40
7 purchase totals =	$689.69		$747.6832	$747.68	$747.65	$747.70