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	$172.70	4.237%	$180.0173	$180.02	$180.00	$180.00
Purchase #2	$154.43	7.158%	$165.4841	$165.48	$165.50	$165.50
Purchase #3	$240.94	3.708%	$249.8741	$249.87	$249.85	$249.90
Purchase #4	$56.99	9.614%	$62.469	$62.47	$62.45	$62.50
Purchase #5	$80.27	11.704%	$89.6648	$89.66	$89.65	$89.70
Purchase #6	$7.41	6.634%	$7.9016	$7.90	$7.90	$7.90
Purchase #7	$237.64	12.275%	$266.8103	$266.81	$266.80	$266.80
7 purchase totals =	$950.38		$1,022.2212	$1,022.21	$1,022.15	$1,022.30