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	$134.56	12.409%	$151.2576	$151.26	$151.25	$151.30
Purchase #2	$97.59	6.535%	$103.9675	$103.97	$103.95	$104.00
Purchase #3	$140.30	11.204%	$156.0192	$156.02	$156.00	$156.00
Purchase #4	$99.47	10.435%	$109.8497	$109.85	$109.85	$109.80
Purchase #5	$78.39	6.730%	$83.6656	$83.67	$83.65	$83.70
Purchase #6	$32.53	7.135%	$34.851	$34.85	$34.85	$34.90
Purchase #7	$165.92	13.367%	$188.0985	$188.10	$188.10	$188.10
7 purchase totals =	$748.76		$827.7091	$827.72	$827.65	$827.80