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	$188.41	6.495%	$200.6472	$200.65	$200.65	$200.60
Purchase #2	$38.27	10.503%	$42.2895	$42.29	$42.30	$42.30
Purchase #3	$119.50	5.278%	$125.8072	$125.81	$125.80	$125.80
Purchase #4	$41.63	9.385%	$45.537	$45.54	$45.55	$45.50
Purchase #5	$245.92	8.559%	$266.9683	$266.97	$266.95	$267.00
Purchase #6	$18.60	6.796%	$19.8641	$19.86	$19.85	$19.90
Purchase #7	$73.36	7.575%	$78.917	$78.92	$78.90	$78.90
7 purchase totals =	$725.69		$780.0303	$780.04	$780.00	$780.00