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	$84.34	8.361%	$91.3917	$91.39	$91.40	$91.40
Purchase #2	$131.77	12.779%	$148.6089	$148.61	$148.60	$148.60
Purchase #3	$116.83	12.743%	$131.7176	$131.72	$131.70	$131.70
Purchase #4	$19.36	8.504%	$21.0064	$21.01	$21.00	$21.00
Purchase #5	$171.52	5.130%	$180.319	$180.32	$180.30	$180.30
Purchase #6	$138.88	5.443%	$146.4392	$146.44	$146.45	$146.40
Purchase #7	$189.32	11.502%	$211.0956	$211.10	$211.10	$211.10
7 purchase totals =	$852.02		$930.5784	$930.59	$930.55	$930.50