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	$84.89	9.412%	$92.8798	$92.88	$92.90	$92.90
Purchase #2	$72.60	7.590%	$78.1103	$78.11	$78.10	$78.10
Purchase #3	$70.59	8.781%	$76.7885	$76.79	$76.80	$76.80
Purchase #4	$60.87	10.846%	$67.472	$67.47	$67.45	$67.50
Purchase #5	$85.51	5.354%	$90.0882	$90.09	$90.10	$90.10
Purchase #6	$139.59	8.159%	$150.9791	$150.98	$151.00	$151.00
Purchase #7	$238.44	8.514%	$258.7408	$258.74	$258.75	$258.70
7 purchase totals =	$752.49		$815.0587	$815.06	$815.10	$815.10