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	$7.97	9.102%	$8.6954	$8.70	$8.70	$8.70
Purchase #2	$142.65	6.847%	$152.4172	$152.42	$152.40	$152.40
Purchase #3	$189.40	10.787%	$209.8306	$209.83	$209.85	$209.80
Purchase #4	$32.56	10.593%	$36.0091	$36.01	$36.00	$36.00
Purchase #5	$85.59	4.538%	$89.4741	$89.47	$89.45	$89.50
Purchase #6	$109.69	5.160%	$115.35	$115.35	$115.35	$115.40
Purchase #7	$168.45	9.503%	$184.4578	$184.46	$184.45	$184.50
7 purchase totals =	$736.31		$796.2342	$796.24	$796.20	$796.30