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	$112.90	5.757%	$119.3997	$119.40	$119.40	$119.40
Purchase #2	$49.50	13.668%	$56.2657	$56.27	$56.25	$56.30
Purchase #3	$174.54	3.331%	$180.3539	$180.35	$180.35	$180.40
Purchase #4	$111.93	12.139%	$125.5172	$125.52	$125.50	$125.50
Purchase #5	$100.46	3.405%	$103.8807	$103.88	$103.90	$103.90
Purchase #6	$23.61	8.110%	$25.5248	$25.52	$25.50	$25.50
Purchase #7	$173.89	4.488%	$181.6942	$181.69	$181.70	$181.70
7 purchase totals =	$746.83		$792.6362	$792.63	$792.60	$792.70