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	$109.82	12.520%	$123.5695	$123.57	$123.55	$123.60
Purchase #2	$215.44	13.722%	$245.0027	$245.00	$245.00	$245.00
Purchase #3	$36.54	9.476%	$40.0025	$40.00	$40.00	$40.00
Purchase #4	$137.65	9.704%	$151.0076	$151.01	$151.00	$151.00
Purchase #5	$152.64	6.579%	$162.6822	$162.68	$162.70	$162.70
Purchase #6	$160.34	12.230%	$179.9496	$179.95	$179.95	$179.90
Purchase #7	$114.57	5.520%	$120.8943	$120.89	$120.90	$120.90
7 purchase totals =	$927.00		$1,023.1084	$1,023.10	$1,023.10	$1,023.10