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	$104.50	9.681%	$114.6166	$114.62	$114.60	$114.60
Purchase #2	$45.71	4.663%	$47.8415	$47.84	$47.85	$47.80
Purchase #3	$41.53	9.777%	$45.5904	$45.59	$45.60	$45.60
Purchase #4	$173.74	13.348%	$196.9308	$196.93	$196.95	$196.90
Purchase #5	$113.98	8.592%	$123.7732	$123.77	$123.75	$123.80
Purchase #6	$42.96	8.248%	$46.5033	$46.50	$46.50	$46.50
Purchase #7	$232.57	5.641%	$245.6893	$245.69	$245.70	$245.70
7 purchase totals =	$754.99		$820.9451	$820.94	$820.95	$820.90