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	$127.83	13.740%	$145.3938	$145.39	$145.40	$145.40
Purchase #2	$124.27	7.836%	$134.0078	$134.01	$134.00	$134.00
Purchase #3	$151.98	11.548%	$169.5307	$169.53	$169.55	$169.50
Purchase #4	$23.55	5.713%	$24.8954	$24.90	$24.90	$24.90
Purchase #5	$21.83	13.832%	$24.8495	$24.85	$24.85	$24.80
Purchase #6	$196.55	11.197%	$218.5577	$218.56	$218.55	$218.60
Purchase #7	$170.90	9.802%	$187.6516	$187.65	$187.65	$187.70
7 purchase totals =	$816.91		$904.8865	$904.89	$904.90	$904.90