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	$102.79	6.221%	$109.1846	$109.18	$109.20	$109.20
Purchase #2	$179.90	4.296%	$187.6285	$187.63	$187.65	$187.60
Purchase #3	$17.38	5.365%	$18.3124	$18.31	$18.30	$18.30
Purchase #4	$182.82	3.145%	$188.5697	$188.57	$188.55	$188.60
Purchase #5	$225.41	5.660%	$238.1682	$238.17	$238.15	$238.20
Purchase #6	$189.83	7.369%	$203.8186	$203.82	$203.80	$203.80
Purchase #7	$182.33	7.649%	$196.2764	$196.28	$196.30	$196.30
7 purchase totals =	$1,080.46		$1,141.9584	$1,141.96	$1,141.95	$1,142.00