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	$109.81	12.177%	$123.1816	$123.18	$123.20	$123.20
Purchase #2	$39.40	8.760%	$42.8514	$42.85	$42.85	$42.90
Purchase #3	$130.56	3.102%	$134.61	$134.61	$134.60	$134.60
Purchase #4	$155.70	9.742%	$170.8683	$170.87	$170.85	$170.90
Purchase #5	$180.45	4.450%	$188.48	$188.48	$188.50	$188.50
Purchase #6	$41.31	13.529%	$46.8988	$46.90	$46.90	$46.90
Purchase #7	$202.72	13.418%	$229.921	$229.92	$229.90	$229.90
7 purchase totals =	$859.95		$936.8111	$936.81	$936.80	$936.90