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	$111.47	10.695%	$123.3917	$123.39	$123.40	$123.40
Purchase #2	$121.63	12.514%	$136.8508	$136.85	$136.85	$136.90
Purchase #3	$160.98	12.213%	$180.6405	$180.64	$180.65	$180.60
Purchase #4	$134.92	5.374%	$142.1706	$142.17	$142.15	$142.20
Purchase #5	$194.41	8.141%	$210.2369	$210.24	$210.25	$210.20
Purchase #6	$29.35	6.806%	$31.3476	$31.35	$31.35	$31.30
Purchase #7	$177.33	6.161%	$188.2553	$188.26	$188.25	$188.30
7 purchase totals =	$930.09		$1,012.8934	$1,012.90	$1,012.90	$1,012.90