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	$182.89	4.439%	$191.0085	$191.01	$191.00	$191.00
Purchase #2	$94.80	5.257%	$99.7836	$99.78	$99.80	$99.80
Purchase #3	$75.46	8.391%	$81.7918	$81.79	$81.80	$81.80
Purchase #4	$200.40	3.280%	$206.9731	$206.97	$206.95	$207.00
Purchase #5	$39.47	7.212%	$42.3166	$42.32	$42.30	$42.30
Purchase #6	$101.52	6.531%	$108.1503	$108.15	$108.15	$108.20
Purchase #7	$82.96	3.134%	$85.56	$85.56	$85.55	$85.60
7 purchase totals =	$777.50		$815.5839	$815.58	$815.55	$815.70