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	$108.33	8.689%	$117.7428	$117.74	$117.75	$117.70
Purchase #2	$139.56	13.547%	$158.4662	$158.47	$158.45	$158.50
Purchase #3	$104.56	7.334%	$112.2284	$112.23	$112.25	$112.20
Purchase #4	$220.54	8.199%	$238.6221	$238.62	$238.60	$238.60
Purchase #5	$77.29	12.276%	$86.7781	$86.78	$86.80	$86.80
Purchase #6	$93.69	11.736%	$104.6855	$104.69	$104.70	$104.70
Purchase #7	$162.35	13.486%	$184.2445	$184.24	$184.25	$184.20
7 purchase totals =	$906.32		$1,002.7676	$1,002.77	$1,002.80	$1,002.70