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	$108.69	13.666%	$123.5436	$123.54	$123.55	$123.50
Purchase #2	$104.49	5.130%	$109.8503	$109.85	$109.85	$109.90
Purchase #3	$238.69	6.628%	$254.5104	$254.51	$254.50	$254.50
Purchase #4	$184.98	13.292%	$209.5675	$209.57	$209.55	$209.60
Purchase #5	$37.38	11.789%	$41.7867	$41.79	$41.80	$41.80
Purchase #6	$219.58	3.112%	$226.4133	$226.41	$226.40	$226.40
Purchase #7	$148.56	5.361%	$156.5243	$156.52	$156.50	$156.50
7 purchase totals =	$1,042.37		$1,122.1961	$1,122.19	$1,122.15	$1,122.20