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	$31.46	10.665%	$34.8152	$34.82	$34.80	$34.80
Purchase #2	$180.70	4.263%	$188.4032	$188.40	$188.40	$188.40
Purchase #3	$136.61	6.563%	$145.5757	$145.58	$145.60	$145.60
Purchase #4	$85.38	9.326%	$93.3425	$93.34	$93.35	$93.30
Purchase #5	$237.69	7.641%	$255.8519	$255.85	$255.85	$255.90
Purchase #6	$146.86	3.741%	$152.354	$152.35	$152.35	$152.40
Purchase #7	$126.65	3.543%	$131.1372	$131.14	$131.15	$131.10
7 purchase totals =	$945.35		$1,001.4797	$1,001.48	$1,001.50	$1,001.50