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	$55.66	3.420%	$57.5636	$57.56	$57.55	$57.60
Purchase #2	$197.84	6.811%	$211.3149	$211.31	$211.30	$211.30
Purchase #3	$37.28	9.653%	$40.8786	$40.88	$40.90	$40.90
Purchase #4	$128.42	9.153%	$140.1743	$140.17	$140.15	$140.20
Purchase #5	$231.58	13.365%	$262.5307	$262.53	$262.55	$262.50
Purchase #6	$31.70	5.708%	$33.5094	$33.51	$33.50	$33.50
Purchase #7	$216.80	7.405%	$232.854	$232.85	$232.85	$232.90
7 purchase totals =	$899.28		$978.8255	$978.81	$978.80	$978.90